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2479 lines
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HTML
2479 lines
88 KiB
HTML
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<meta name="author" content="Peter Dimov">
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<title>Boost.Variant2: A never valueless variant type</title>
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</head>
|
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<body class="article toc2 toc-left">
|
|
<div id="header">
|
|
<h1>Boost.Variant2: A never valueless variant type</h1>
|
|
<div class="details">
|
|
<span id="author" class="author">Peter Dimov</span><br>
|
|
</div>
|
|
<div id="toc" class="toc2">
|
|
<div id="toctitle">Table of Contents</div>
|
|
<ul class="sectlevel1">
|
|
<li><a href="#overview">Overview</a>
|
|
<ul class="sectlevel2">
|
|
<li><a href="#overview_description">Description</a></li>
|
|
<li><a href="#overview_usage_examples">Usage Examples</a></li>
|
|
<li><a href="#overview_construction_and_assignment">Construction and Assignment</a></li>
|
|
<li><a href="#overview_inspecting_the_value">Inspecting the Value</a></li>
|
|
<li><a href="#overview_visitation">Visitation</a></li>
|
|
<li><a href="#overview_default_construction">Default Construction</a></li>
|
|
</ul>
|
|
</li>
|
|
<li><a href="#reference">Reference</a>
|
|
<ul class="sectlevel2">
|
|
<li><a href="#ref_boostvariant2variant_hpp"><boost/variant2/variant.hpp></a>
|
|
<ul class="sectlevel3">
|
|
<li><a href="#ref_synopsis">Synopsis</a></li>
|
|
<li><a href="#ref_variant">variant</a>
|
|
<ul class="sectlevel4">
|
|
<li><a href="#ref_constructors">Constructors</a></li>
|
|
<li><a href="#ref_destructor">Destructor</a></li>
|
|
<li><a href="#ref_assignment">Assignment</a></li>
|
|
<li><a href="#ref_modifiers">Modifiers</a></li>
|
|
<li><a href="#ref_value_status">Value Status</a></li>
|
|
<li><a href="#ref_swap">Swap</a></li>
|
|
<li><a href="#ref_converting_constructors_extension">Converting Constructors (extension)</a></li>
|
|
<li><a href="#ref_subset_extension">Subset (extension)</a></li>
|
|
</ul>
|
|
</li>
|
|
<li><a href="#ref_variant_alternative">variant_alternative</a></li>
|
|
<li><a href="#ref_holds_alternative">holds_alternative</a></li>
|
|
<li><a href="#ref_get">get</a></li>
|
|
<li><a href="#ref_get_if">get_if</a></li>
|
|
<li><a href="#ref_relational_operators">Relational Operators</a></li>
|
|
<li><a href="#ref_visit">visit</a></li>
|
|
<li><a href="#ref_swap_2">swap</a></li>
|
|
<li><a href="#ref_bad_variant_access">bad_variant_access</a></li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
<li><a href="#copyright">Copyright and License</a></li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div id="content">
|
|
<div class="sect1">
|
|
<h2 id="overview">Overview</h2>
|
|
<div class="sectionbody">
|
|
<div class="sect2">
|
|
<h3 id="overview_description">Description</h3>
|
|
<div class="paragraph">
|
|
<p>This library implements a type-safe discriminated/tagged union type,
|
|
<code>variant<T…​></code>, that is API-compatible with the C++17 Standard’s
|
|
<a href="http://en.cppreference.com/w/cpp/utility/variant"><code>std::variant<T…​></code></a>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>A <code>variant<T1, T2, …​, Tn></code> variable can hold a value of any of the
|
|
types <code>T1</code>, <code>T2</code>, …​, <code>Tn</code>. For example,
|
|
<code>variant<int64_t, double, std::string></code> can hold an <code>int64_t</code> value, a
|
|
<code>double</code> value, or a <code>string</code> value.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Such a type is sometimes called a "tagged union", because it’s roughly
|
|
equivalent to</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>struct V
|
|
{
|
|
enum tag { tag_int64_t, tag_double, tag_string };
|
|
|
|
tag tag_;
|
|
|
|
union
|
|
{
|
|
int64_t i_;
|
|
double d_;
|
|
std::string s_;
|
|
};
|
|
};</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="overview_usage_examples">Usage Examples</h3>
|
|
<div class="paragraph">
|
|
<p>Variants can be used to represent dynamically-typed values. A configuration
|
|
file of the form</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>server.host=test.example.com
|
|
server.port=9174
|
|
cache.max_load=0.7</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>can be represented as <code>std::map<std::string, variant<int64_t, double,
|
|
std::string>></code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Variants can also represent polymorphism. To take a classic example, a
|
|
polymorphic collection of shapes:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>#define _USE_MATH_DEFINES
|
|
#include <iostream>
|
|
#include <vector>
|
|
#include <memory>
|
|
#include <cmath>
|
|
|
|
class Shape
|
|
{
|
|
public:
|
|
|
|
virtual ~Shape() = default;
|
|
virtual double area() const = 0;
|
|
};
|
|
|
|
class Rectangle: public Shape
|
|
{
|
|
private:
|
|
|
|
double width_, height_;
|
|
|
|
public:
|
|
|
|
Rectangle( double width, double height ):
|
|
width_( width ), height_( height ) {}
|
|
|
|
virtual double area() const { return width_ * height_; }
|
|
};
|
|
|
|
class Circle: public Shape
|
|
{
|
|
private:
|
|
|
|
double radius_;
|
|
|
|
public:
|
|
|
|
explicit Circle( double radius ): radius_( radius ) {}
|
|
virtual double area() const { return M_PI * radius_ * radius_; }
|
|
};
|
|
|
|
double total_area( std::vector<std::unique_ptr<Shape>> const & v )
|
|
{
|
|
double s = 0.0;
|
|
|
|
for( auto const& p: v )
|
|
{
|
|
s += p->area();
|
|
}
|
|
|
|
return s;
|
|
}
|
|
|
|
int main()
|
|
{
|
|
std::vector<std::unique_ptr<Shape>> v;
|
|
|
|
v.push_back( std::unique_ptr<Shape>( new Circle( 1.0 ) ) );
|
|
v.push_back( std::unique_ptr<Shape>( new Rectangle( 2.0, 3.0 ) ) );
|
|
|
|
std::cout << "Total area: " << total_area( v ) << std::endl;
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>can instead be represented as a collection of <code>variant<Rectangle, Circle></code>
|
|
values. This requires the possible <code>Shape</code> types be known in advance, as is
|
|
often the case. In return, we no longer need virtual functions, or to allocate
|
|
the values on the heap with <code>new Rectangle</code> and <code>new Circle</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>#define _USE_MATH_DEFINES
|
|
#include <iostream>
|
|
#include <vector>
|
|
#include <cmath>
|
|
|
|
#include <boost/variant2/variant.hpp>
|
|
using namespace boost::variant2;
|
|
|
|
struct Rectangle
|
|
{
|
|
double width_, height_;
|
|
double area() const { return width_ * height_; }
|
|
};
|
|
|
|
struct Circle
|
|
{
|
|
double radius_;
|
|
double area() const { return M_PI * radius_ * radius_; }
|
|
};
|
|
|
|
double total_area( std::vector<variant<Rectangle, Circle>> const & v )
|
|
{
|
|
double s = 0.0;
|
|
|
|
for( auto const& x: v )
|
|
{
|
|
s += visit( []( auto const& y ){ return y.area(); }, x );
|
|
}
|
|
|
|
return s;
|
|
}
|
|
|
|
int main()
|
|
{
|
|
std::vector<variant<Rectangle, Circle>> v;
|
|
|
|
v.push_back( Circle{ 1.0 } );
|
|
v.push_back( Rectangle{ 2.0, 3.0 } );
|
|
|
|
std::cout << "Total area: " << total_area( v ) << std::endl;
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="overview_construction_and_assignment">Construction and Assignment</h3>
|
|
<div class="paragraph">
|
|
<p>If we look at the</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code> v.push_back( Circle{ 1.0 } );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>line, we can deduce that <code>variant<Rectangle, Circle></code> can be (implicitly)
|
|
constructed from <code>Circle</code> (and <code>Rectangle</code>), and indeed it can. It can also
|
|
be assigned a <code>Circle</code> or a <code>Rectangle</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>variant<Rectangle, Circle> v = Circle{ 1.0 }; // v holds Circle
|
|
v = Rectangle{ 2.0, 3.0 }; // v now holds Rectangle</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>If we try to construct <code>variant<int, float></code> from something that is neither
|
|
<code>int</code> nor <code>float</code>, say, <code>(short)1</code>, the behavior is "as if" the <code>variant</code> has
|
|
declared two constructors,</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>variant::variant(int x);
|
|
variant::variant(float x);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>and the standard overload resolution rules are used to pick the one that will
|
|
be used. So <code>variant<int, float>((short)1)</code> will hold an <code>int</code>.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="overview_inspecting_the_value">Inspecting the Value</h3>
|
|
<div class="paragraph">
|
|
<p>Putting values into a <code>variant</code> is easy, but taking them out is necessarily a
|
|
bit more convoluted. It’s not possible for <code>variant<int, float></code> to define a
|
|
member function <code>get() const</code>, because such a function will need its return
|
|
type fixed at compile time, and whether the correct return type is <code>int</code> or
|
|
<code>float</code> will only become known at run time.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>There are a few ways around that. First, there is the accessor member function</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>std::size_t variant::index() const noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>that returns the zero-based index of the current type. For <code>variant<int,
|
|
float></code>, it will return <code>0</code> for <code>int</code> and <code>1</code> for <code>float</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Once we have the index, we can use the free function <code>get<N></code> to obtain the
|
|
value. Since we’re passing the type index to <code>get</code>, it knows what to return.
|
|
<code>get<0>(v)</code> will return <code>int</code>, and <code>get<1>(v)</code> will return <code>float</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>void f( variant<int, float> const& v )
|
|
{
|
|
switch( v.index() )
|
|
{
|
|
case 0:
|
|
|
|
// use get<0>(v)
|
|
break;
|
|
|
|
case 1:
|
|
|
|
// use get<1>(v)
|
|
break;
|
|
|
|
default:
|
|
|
|
assert(false); // never happens
|
|
}
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>If we call <code>get<0>(v)</code>, and <code>v.index()</code> is not currently <code>0</code>, an exception
|
|
(of type <code>bad_variant_access</code>) will be thrown.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>An alternative approach is to use <code>get<int>(v)</code> or <code>get<float>(v)</code>. This
|
|
works similarly.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Another alternative that avoids the possibility of <code>bad_variant_access</code> is
|
|
to use <code>get_if</code>. Instead of a reference to the contained value, it returns
|
|
a pointer to it, returning <code>nullptr</code> to indicate type mismatch. <code>get_if</code>
|
|
takes a pointer to the <code>variant</code>, so in our example we’ll use something along
|
|
the following lines:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>void f( variant<int, float> const& v )
|
|
{
|
|
if( int const * p = get_if<int>(&v) )
|
|
{
|
|
// use *p
|
|
}
|
|
else if( float const * p = get_if<float>(&v) )
|
|
{
|
|
// use *p
|
|
}
|
|
else
|
|
{
|
|
assert(false); // never happens
|
|
}
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="overview_visitation">Visitation</h3>
|
|
<div class="paragraph">
|
|
<p>Last but not least, there’s <code>visit</code>. <code>visit(f, v)</code> calls the a function object
|
|
<code>f</code> with the value contained in the <code>variant</code> <code>v</code> and returns the result. When
|
|
<code>v</code> is <code>variant<int, float></code>, it will call <code>f</code> with either an <code>int</code> or a
|
|
<code>float</code>. The function object must be prepared to accept both.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>In practice, this can be achieved by having the function take a type that can
|
|
be passed either <code>int</code> or <code>float</code>, such as <code>double</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>double f( double x ) { return x; }
|
|
|
|
double g( variant<int, float> const& v )
|
|
{
|
|
return visit( f, v );
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>By using a function object with an overloaded <code>operator()</code>:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>struct F
|
|
{
|
|
void operator()(int x) const { /* use x */ }
|
|
void operator()(float x) const { /* use x */ }
|
|
};
|
|
|
|
void g( variant<int, float> const& v )
|
|
{
|
|
visit( F(), v );
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Or by using a polymorphic lambda, as we did in our <code>Circle</code>/<code>Rectangle</code>
|
|
example:</p>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>void g( variant<int, float> const& v )
|
|
{
|
|
visit( [&]( auto const& x ){ std::cout << x << std::endl; }, v );
|
|
}</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p><code>visit</code> can also take more than one <code>variant</code>. <code>visit(f, v1, v2)</code> calls
|
|
<code>f(x1, x2)</code>, where <code>x1</code> is the value contained in <code>v1</code> and <code>x2</code> is the value
|
|
in <code>v2</code>.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="overview_default_construction">Default Construction</h3>
|
|
<div class="paragraph">
|
|
<p>The default constructor of <code>variant</code> value-initializes the first type in
|
|
the list. <code>variant<int, float>{}</code> holds <code>0</code> (of type <code>int</code>), and
|
|
<code>variant<float, int>{}</code> holds <code>0.0f</code>.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This is usually the desired behavior. However, in cases such as
|
|
<code>variant<std::mutex, std::recursive_mutex></code>, one might legitimately wish to
|
|
avoid constructing a <code>std::mutex</code> by default. A provided type, <code>monostate</code>,
|
|
can be used as the first type in those scenarios. <code>variant<monostate,
|
|
std::mutex, std::recursive_mutex></code> will default-construct a <code>monostate</code>,
|
|
which is basically a no-op, as <code>monostate</code> is effectively an empty <code>struct</code>.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="reference">Reference</h2>
|
|
<div class="sectionbody">
|
|
<div class="sect2">
|
|
<h3 id="ref_boostvariant2variant_hpp"><boost/variant2/variant.hpp></h3>
|
|
<div class="sect3">
|
|
<h4 id="ref_synopsis">Synopsis</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>namespace boost {
|
|
namespace variant2 {
|
|
|
|
// in_place_type
|
|
|
|
template<class T> struct in_place_type_t {};
|
|
template<class T> constexpr in_place_type_t<T> in_place_type{};
|
|
|
|
// in_place_index
|
|
|
|
template<std::size_t I> struct in_place_index_t {};
|
|
template<std::size_t I> constexpr in_place_index_t<I> in_place_index{};
|
|
|
|
// variant
|
|
|
|
template<class... T> class variant;
|
|
|
|
// variant_size
|
|
|
|
template<class T> struct variant_size {};
|
|
|
|
template<class T> struct variant_size<T const>: variant_size<T> {};
|
|
template<class T> struct variant_size<T volatile>: variant_size<T> {};
|
|
template<class T> struct variant_size<T const volatile>: variant_size<T> {};
|
|
|
|
template<class T> struct variant_size<T&>: variant_size<T> {}; // extension
|
|
template<class T> struct variant_size<T&&>: variant_size<T> {}; // extension
|
|
|
|
template<class T>
|
|
inline constexpr size_t variant_size_v = variant_size<T>::value;
|
|
|
|
template<class... T>
|
|
struct variant_size<variant<T...>>:
|
|
std::integral_constant<std::size_t, sizeof...(T)> {};
|
|
|
|
// variant_alternative
|
|
|
|
template<size_t I, class T> struct variant_alternative {};
|
|
|
|
template<size_t I, class T> struct variant_alternative<I, T const>;
|
|
template<size_t I, class T> struct variant_alternative<I, T volatile>;
|
|
template<size_t I, class T> struct variant_alternative<I, T const volatile>;
|
|
|
|
template<size_t I, class T> struct variant_alternative<I, T&>; // extension
|
|
template<size_t I, class T> struct variant_alternative<I, T&&>; // extension
|
|
|
|
template<size_t I, class T>
|
|
using variant_alternative_t = typename variant_alternative<I, T>::type;
|
|
|
|
template<size_t I, class... T>
|
|
struct variant_alternative<I, variant<T...>>;
|
|
|
|
// variant_npos
|
|
|
|
constexpr std::size_t variant_npos = -1;
|
|
|
|
// holds_alternative
|
|
|
|
template<class U, class... T>
|
|
constexpr bool holds_alternative(const variant<T...>& v) noexcept;
|
|
|
|
// get
|
|
|
|
template<size_t I, class... T>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
get(variant<T...>& v);
|
|
template<size_t I, class... T>
|
|
constexpr variant_alternative_t<I, variant<T...>>&&
|
|
get(variant<T...>&& v);
|
|
template<size_t I, class... T>
|
|
constexpr const variant_alternative_t<I, variant<T...>>&
|
|
get(const variant<T...>& v);
|
|
template<size_t I, class... T>
|
|
constexpr const variant_alternative_t<I, variant<T...>>&&
|
|
get(const variant<T...>&& v);
|
|
|
|
template<class U, class... T>
|
|
constexpr U& get(variant<T...>& v);
|
|
template<class U, class... T>
|
|
constexpr U&& get(variant<T...>&& v);
|
|
template<class U, class... T>
|
|
constexpr const U& get(const variant<T...>& v);
|
|
template<class U, class... T>
|
|
constexpr const U&& get(const variant<T...>&& v);
|
|
|
|
// get_if
|
|
|
|
template<size_t I, class... T>
|
|
constexpr add_pointer_t<variant_alternative_t<I, variant<T...>>>
|
|
get_if(variant<T...>* v) noexcept;
|
|
template<size_t I, class... T>
|
|
constexpr add_pointer_t<const variant_alternative_t<I, variant<T...>>>
|
|
get_if(const variant<T...>* v) noexcept;
|
|
|
|
template<class U, class... T>
|
|
constexpr add_pointer_t<U>
|
|
get_if(variant<T...>* v) noexcept;
|
|
template<class U, class... T>
|
|
constexpr add_pointer_t<const U>
|
|
get_if(const variant<T...>* v) noexcept;
|
|
|
|
// relational operators
|
|
|
|
template<class... T>
|
|
constexpr bool operator==(const variant<T...>& v, const variant<T...>& w);
|
|
template<class... T>
|
|
constexpr bool operator!=(const variant<T...>& v, const variant<T...>& w);
|
|
template<class... T>
|
|
constexpr bool operator<(const variant<T...>& v, const variant<T...>& w);
|
|
template<class... T>
|
|
constexpr bool operator>(const variant<T...>& v, const variant<T...>& w);
|
|
template<class... T>
|
|
constexpr bool operator<=(const variant<T...>& v, const variant<T...>& w);
|
|
template<class... T>
|
|
constexpr bool operator>=(const variant<T...>& v, const variant<T...>& w);
|
|
|
|
// visit
|
|
|
|
template<class F, class... V>
|
|
constexpr /*see below*/ visit(F&& f, V&&... v);
|
|
|
|
// monostate
|
|
|
|
struct monostate {};
|
|
|
|
constexpr bool operator==(monostate, monostate) noexcept { return true; }
|
|
constexpr bool operator!=(monostate, monostate) noexcept { return false; }
|
|
constexpr bool operator<(monostate, monostate) noexcept { return false; }
|
|
constexpr bool operator>(monostate, monostate) noexcept { return false; }
|
|
constexpr bool operator<=(monostate, monostate) noexcept { return true; }
|
|
constexpr bool operator>=(monostate, monostate) noexcept { return true; }
|
|
|
|
// swap
|
|
|
|
template<class... T>
|
|
void swap(variant<T...>& v, variant<T...>& w) noexcept( /*see below*/ );
|
|
|
|
// bad_variant_access
|
|
|
|
class bad_variant_access;
|
|
|
|
} // namespace variant2
|
|
} // namespace boost</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_variant">variant</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>namespace boost {
|
|
namespace variant2 {
|
|
|
|
template<class... T> class variant
|
|
{
|
|
public:
|
|
|
|
// constructors
|
|
|
|
constexpr variant() noexcept( /*see below*/ );
|
|
|
|
constexpr variant( variant const & r ) noexcept( /*see below*/ );
|
|
constexpr variant( variant&& r ) noexcept( /*see below*/ );
|
|
|
|
template<class U>
|
|
constexpr variant( U&& u ) noexcept( /*see below*/ );
|
|
|
|
template<class U, class... A>
|
|
constexpr explicit variant( in_place_type_t<U>, A&&... a );
|
|
template<class U, class V, class... A>
|
|
constexpr explicit variant( in_place_type_t<U>,
|
|
std::initializer_list<V> il, A&&... a );
|
|
|
|
template<size_t I, class... A>
|
|
constexpr explicit variant( in_place_index_t<I>, A&&... a );
|
|
template<size_t I, class V, class... A>
|
|
constexpr explicit variant( in_place_index_t<I>,
|
|
std::initializer_list<V> il, A&&... a );
|
|
|
|
// destructor
|
|
|
|
~variant();
|
|
|
|
// assignment
|
|
|
|
constexpr variant& operator=( variant const & r ) noexcept( /*see below*/ );
|
|
constexpr variant& operator=( variant&& r ) noexcept( /*see below*/ );
|
|
|
|
template<class U> constexpr variant& operator=( U&& u ) noexcept( /*see below*/ );
|
|
|
|
// modifiers
|
|
|
|
template<class U, class... A>
|
|
constexpr U& emplace( A&&... a );
|
|
template<class U, class V, class... A>
|
|
constexpr U& emplace( std::initializer_list<V> il, A&&... a );
|
|
|
|
template<size_t I, class... A>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
emplace( A&&... a );
|
|
template<size_t I, class V, class... A>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
emplace( std::initializer_list<V> il, A&&... a );
|
|
|
|
// value status
|
|
|
|
constexpr bool valueless_by_exception() const noexcept;
|
|
constexpr size_t index() const noexcept;
|
|
|
|
// swap
|
|
|
|
void swap( variant& r ) noexcept( /*see below*/ );
|
|
|
|
// converting constructors (extension)
|
|
|
|
template<class... U> variant( variant<U...> const& r )
|
|
noexcept( /*see below*/ );
|
|
|
|
template<class... U> variant( variant<U...>&& r )
|
|
noexcept( /*see below*/ );
|
|
|
|
// subset (extension)
|
|
|
|
template<class... U> constexpr variant<U...> subset() & ;
|
|
template<class... U> constexpr variant<U...> subset() && ;
|
|
template<class... U> constexpr variant<U...> subset() const& ;
|
|
template<class... U> constexpr variant<U...> subset() const&& ;
|
|
};
|
|
|
|
} // namespace variant2
|
|
} // namespace boost</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_constructors">Constructors</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr variant() noexcept( std::is_nothrow_default_constructible_v<T0> );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Constructs a <code>variant</code> holding a value-initialized value of
|
|
type <code>T0</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == 0</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the value-initialization of <code>T0</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
<code>std::is_default_constructible_v<T0></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr variant( variant const & w )
|
|
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the variant to hold the same alternative and value as
|
|
<code>w</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
<code>std::is_copy_constructible_v<Ti></code> is <code>true</code> for all <code>i</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr variant( variant&& w )
|
|
noexcept( mp_all<std::is_nothrow_move_constructible<T>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the variant to hold the same alternative and value as
|
|
<code>w</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the move-initialization of the contained
|
|
value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
<code>std::is_move_constructible_v<Ti></code> is <code>true</code> for all <code>i</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U> constexpr variant( U&& u ) noexcept(/*see below*/);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>Tj</code> be a type that is determined as follows: build an imaginary function
|
|
<code>FUN(Ti)</code> for each alternative type <code>Ti</code>. The overload <code>FUN(Tj)</code> selected by
|
|
overload resolution for the expression <code>FUN(std::forward<U>(u))</code> defines the
|
|
alternative <code>Tj</code> which is the type of the contained value after construction.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes <code>*this</code> to hold the alternative type <code>Tj</code> and
|
|
initializes the contained value from <code>std::forward<U>(u)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>holds_alternative<Tj>(*this)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>The expression inside <code>noexcept</code> is equivalent to
|
|
<code>std::is_nothrow_constructible_v<Tj, U></code>. This function does not participate in
|
|
overload resolution unless</p>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>sizeof…​(T)</code> is nonzero,</p>
|
|
</li>
|
|
<li>
|
|
<p><code>std::is_same_v<std::remove_cvref_t<U>, variant></code> is <code>false</code>,</p>
|
|
</li>
|
|
<li>
|
|
<p><code>std::remove_cvref_t<U></code> is neither a specialization of <code>in_place_type_t</code> nor a
|
|
specialization of <code>in_place_index_t</code>,</p>
|
|
</li>
|
|
<li>
|
|
<p><code>std::is_constructible_v<Tj, U></code> is <code>true</code>, and</p>
|
|
</li>
|
|
<li>
|
|
<p>the expression <code>FUN(std::forward<U>(u))</code> is well-formed.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... A>
|
|
constexpr explicit variant( in_place_type_t<U>, A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value of type <code>U</code> with the arguments
|
|
<code>std::forward<A>(a)…​</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>holds_alternative<U>(*this)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
there is exactly one occurrence of <code>U</code> in <code>T…​</code> and
|
|
<code>std::is_constructible_v<U, A…​></code> is true.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class V, class... A>
|
|
constexpr explicit variant( in_place_type_t<U>, std::initializer_list<V> il,
|
|
A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value of type <code>U</code> with the arguments <code>il</code>,
|
|
<code>std::forward<A>(a)…​</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>holds_alternative<U>(*this)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
there is exactly one occurrence of <code>U</code> in <code>T…​</code> and
|
|
<code>std::is_constructible_v<U, initializer_list<V>&, A…​></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... A>
|
|
constexpr explicit variant( in_place_index_t<I>, A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value of type <code>TI</code> with the arguments
|
|
<code>std::forward<A>(a)…​</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == I</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
<code>I < sizeof…​(T)</code> and <code>std::is_constructible_v<TI, A…​></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class V, class... A>
|
|
constexpr explicit variant( in_place_index_t<I>, std::initializer_list<V> il,
|
|
A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value of type <code>TI</code> with the arguments
|
|
<code>il</code>, <code>std::forward<A>(a)…​</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == I</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
<code>I < sizeof…​(T)</code> and
|
|
<code>std::is_constructible_v<TI, initializer_list<V>&, A…​></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_destructor">Destructor</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>~variant();</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Destroys the currently contained value.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_assignment">Assignment</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr variant& operator=( const variant& r )
|
|
noexcept( mp_all<std::is_nothrow_copy_constructible<T>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>j</code> be <code>r.index()</code>.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p><code>emplace<j>(get<j>(r))</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>*this</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == r.index()</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This operator does not participate in overload resolution unless
|
|
<code>std::is_copy_constructible_v<Ti> && std::is_copy_assignable_v<Ti></code> is
|
|
<code>true</code> for all <code>i</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr variant& operator=( variant&& r )
|
|
noexcept( mp_all<std::is_nothrow_move_constructible<T>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>j</code> be <code>r.index()</code>.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p><code>emplace<j>(get<j>(std::move(r)))</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>*this</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == r.index()</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This operator does not participate in overload resolution unless
|
|
<code>std::is_move_constructible_v<Ti> && std::is_move_assignable_v<Ti></code> is
|
|
<code>true</code> for all <code>i</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U> constexpr variant& operator=( U&& u )
|
|
noexcept( /*see below*/ );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>Tj</code> be a type that is determined as follows: build an imaginary function
|
|
<code>FUN(Ti)</code> for each alternative type <code>Ti</code>. The overload <code>FUN(Tj)</code> selected by
|
|
overload resolution for the expression <code>FUN(std::forward<U>(u))</code> defines the
|
|
alternative <code>Tj</code> which is the type of the contained value after construction.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p><code>emplace<j>(std::forward<U>(u))</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>*this</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == j</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>The expression inside <code>noexcept</code> is <code>std::is_nothrow_constructible_v<Tj, U&&></code>.
|
|
This operator does not participate in overload resolution unless</p>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>std::is_same_v<std::remove_cvref_t<T>, variant></code> is <code>false</code>,</p>
|
|
</li>
|
|
<li>
|
|
<p><code>std::is_constructible_v<Tj, U&&> && std::is_assignable_v<Tj&, U&&></code> is
|
|
<code>true</code>, and</p>
|
|
</li>
|
|
<li>
|
|
<p>the expression <code>FUN(std::forward<U>(u))</code> (with <code>FUN</code> being the
|
|
above-mentioned set of imaginary functions) is well-formed.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_modifiers">Modifiers</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... A>
|
|
constexpr U& emplace( A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>I</code> be the zero-based index of <code>U</code> in <code>T…​</code>.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Equivalent to: <code>return emplace<I>(std::forward<A>(a)…​);</code></p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function shall not participate in overload resolution unless
|
|
<code>std::is_constructible_v<U, A&&…​></code> is <code>true</code> and <code>U</code> occurs exactly once
|
|
in <code>T…​</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class V, class... A>
|
|
constexpr U& emplace( std::initializer_list<V> il, A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>Let <code>I</code> be the zero-based index of <code>U</code> in <code>T…​</code>.</p>
|
|
</div>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Equivalent to: <code>return emplace<I>(il, std::forward<A>(a)…​);</code></p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function shall not participate in overload resolution unless
|
|
<code>std::is_constructible_v<U, std::initializer_list<V>&, A&&…​></code> is <code>true</code>
|
|
and <code>U</code> occurs exactly once in <code>T…​</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... A>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
emplace( A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p><code>I < sizeof…​(T)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Destroys the currently contained value, then initializes a new contained
|
|
value as if using the expression <code>Ti(std::forward<A>(a)…​)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == I</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p>A reference to the new contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Nothing unless the initialization of the new contained value throws.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Exception Safety: </dt>
|
|
<dd>
|
|
<p>Strong. On exception, the contained value is unchanged.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function shall not participate in overload resolution unless
|
|
<code>std::is_constructible_v<Ti, A&&…​></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class V, class... A>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
emplace( std::initializer_list<V> il, A&&... a );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p><code>I < sizeof…​(T)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Destroys the currently contained value, then initializes a new contained
|
|
value as if using the expression <code>Ti(il, std::forward<A>(a)…​)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Ensures: </dt>
|
|
<dd>
|
|
<p><code>index() == I</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p>A reference to the new contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Nothing unless the initialization of the new contained value throws.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Exception Safety: </dt>
|
|
<dd>
|
|
<p>Strong. On exception, the contained value is unchanged.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function shall not participate in overload resolution unless
|
|
<code>std::is_constructible_v<Ti, std::initializer_list<V>&, A&&…​></code> is <code>true</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_value_status">Value Status</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr bool valueless_by_exception() const noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>false</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<div class="admonitionblock note">
|
|
<table>
|
|
<tr>
|
|
<td class="icon">
|
|
<div class="title">Note</div>
|
|
</td>
|
|
<td class="content">
|
|
This function is provided purely for compatibility with <code>std::variant</code>.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>constexpr size_t index() const noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p>The zero-based index of the active alternative.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_swap">Swap</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>void swap( variant& r ) noexcept( mp_all<std::is_nothrow_move_constructible<T>...,
|
|
is_nothrow_swappable<T>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>If <code>index() == r.index()</code>, calls <code>swap(get<I>(*this), get<I>(r))</code>,
|
|
where <code>I</code> is <code>index()</code>.</p>
|
|
</li>
|
|
<li>
|
|
<p>Otherwise, as if
|
|
<code>variant tmp(std::move(*this)); *this = std::move(r); r = std::move(tmp);</code></p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_converting_constructors_extension">Converting Constructors (extension)</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> variant( variant<U...> const& r )
|
|
noexcept( mp_all<std::is_nothrow_copy_constructible<U>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value from the contained value of <code>r</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
all types in <code>U…​</code> are in <code>T…​</code> and
|
|
<code>std::is_copy_constructible_v<Ui>::value</code> is <code>true</code> for all <code>Ui</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> variant( variant<U...>&& r )
|
|
noexcept( mp_all<std::is_nothrow_move_constructible<U>...>::value );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Initializes the contained value from the contained value of
|
|
<code>std::move(r)</code>.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<p>Any exception thrown by the initialization of the contained value.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
all types in <code>U…​</code> are in <code>T…​</code> and
|
|
<code>std::is_move_constructible_v<Ui>::value</code> is <code>true</code> for all <code>Ui</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect4">
|
|
<h5 id="ref_subset_extension">Subset (extension)</h5>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> constexpr variant<U...> subset() & ;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> constexpr variant<U...> subset() const& ;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p>A <code>variant<U…​></code> whose contained value is copy-initialized from
|
|
the contained value of <code>*this</code> and has the same type.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>If the active alternative of <code>*this</code> is not among the types in <code>U…​</code>,
|
|
<code>bad_variant_access</code>.</p>
|
|
</li>
|
|
<li>
|
|
<p>Otherwise, any exception thrown by the initialization of the contained value.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
all types in <code>U…​</code> are in <code>T…​</code> and
|
|
<code>std::is_copy_constructible_v<Ui>::value</code> is <code>true</code> for all <code>Ui</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> constexpr variant<U...> subset() && ;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... U> constexpr variant<U...> subset() const&& ;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p>A <code>variant<U…​></code> whose contained value is move-initialized from
|
|
the contained value of <code>*this</code> and has the same type.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Throws: </dt>
|
|
<dd>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>If the active alternative of <code>*this</code> is not among the types in <code>U…​</code>,
|
|
<code>bad_variant_access</code>.</p>
|
|
</li>
|
|
<li>
|
|
<p>Otherwise, any exception thrown by the initialization of the contained value.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</dd>
|
|
<dt class="hdlist1">Remarks: </dt>
|
|
<dd>
|
|
<p>This function does not participate in overload resolution unless
|
|
all types in <code>U…​</code> are in <code>T…​</code> and
|
|
<code>std::is_move_constructible_v<Ui>::value</code> is <code>true</code> for all <code>Ui</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_variant_alternative">variant_alternative</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class T> struct variant_alternative<I, T const>;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class T> struct variant_alternative<I, T volatile>;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class T> struct variant_alternative<I, T const volatile>;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class T> struct variant_alternative<I, T&>; // extension</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class T> struct variant_alternative<I, T&&>; // extension</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="openblock">
|
|
<div class="content">
|
|
<div class="paragraph">
|
|
<p>If <code>typename variant_alternative<I, T>::type</code> exists and is <code>U</code>,</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p><code>variant_alternative<I, T const>::type</code> is <code>U const</code>;</p>
|
|
</li>
|
|
<li>
|
|
<p><code>variant_alternative<I, T volatile>::type</code> is <code>U volatile</code>;</p>
|
|
</li>
|
|
<li>
|
|
<p><code>variant_alternative<I, T const volatile>::type</code> is <code>U const volatile</code>.</p>
|
|
</li>
|
|
<li>
|
|
<p><code>variant_alternative<I, T&>::type</code> is <code>U&</code>.</p>
|
|
</li>
|
|
<li>
|
|
<p><code>variant_alternative<I, T&&>::type</code> is <code>U&&</code>.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Otherwise, these structs have no member <code>type</code>.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
struct variant_alternative<I, variant<T...>>;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="paragraph">
|
|
<p>When <code>I < sizeof…​(T)</code>, the nested type <code>type</code> is an alias for the <code>I</code>-th
|
|
(zero-based) type in <code>T…​</code>. Otherwise, there is no member <code>type</code>.</p>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_holds_alternative">holds_alternative</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr bool holds_alternative(const variant<T...>& v) noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p>The type <code>U</code> occurs exactly once in <code>T…​</code>. Otherwise, the
|
|
program is ill-formed.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>true</code> if <code>index()</code> is equal to the zero-based index of <code>U</code>
|
|
in <code>T…​</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_get">get</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr variant_alternative_t<I, variant<T...>>&
|
|
get(variant<T...>& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr variant_alternative_t<I, variant<T...>>&&
|
|
get(variant<T...>&& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr const variant_alternative_t<I, variant<T...>>&
|
|
get(const variant<T...>& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr const variant_alternative_t<I, variant<T...>>&&
|
|
get(const variant<T...>&& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>If <code>v.index()</code> is <code>I</code>, returns a reference to the object stored in
|
|
the variant. Otherwise, throws <code>bad_variant_access</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr U& get(variant<T...>& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr U&& get(variant<T...>&& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr const U& get(const variant<T...>& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr const U&& get(const variant<T...>&& v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p>The type <code>U</code> occurs exactly once in <code>T…​</code>. Otherwise, the
|
|
program is ill-formed.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>If <code>v</code> holds a value of type <code>U</code>, returns a reference to that value.
|
|
Otherwise, throws <code>bad_variant_access</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_get_if">get_if</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr add_pointer_t<variant_alternative_t<I, variant<T...>>>
|
|
get_if(variant<T...>* v) noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<size_t I, class... T>
|
|
constexpr add_pointer_t<const variant_alternative_t<I, variant<T...>>>
|
|
get_if(const variant<T...>* v) noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p><code>I < sizeof…​(U)</code>. Otherwise, the program is ill-formed.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>A pointer to the value stored in the variant, if
|
|
<code>v != nullptr && v->index() == I</code>. Otherwise, <code>nullptr</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr add_pointer_t<U>
|
|
get_if(variant<T...>* v) noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class U, class... T>
|
|
constexpr add_pointer_t<const U>
|
|
get_if(const variant<T...>* v) noexcept;</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Requires: </dt>
|
|
<dd>
|
|
<p>The type <code>U</code> occurs exactly once in <code>T…​</code>. Otherwise, the
|
|
program is ill-formed.</p>
|
|
</dd>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Equivalent to: <code>return get_if<I>(v);</code> with <code>I</code> being
|
|
the zero-based index of <code>U</code> in <code>T…​</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_relational_operators">Relational Operators</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator==(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>v.index() == w.index && get<I>(v) == get<I>(w)</code>, where <code>I</code>
|
|
is <code>v.index()</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator!=(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>!(v == w)</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator<(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>v.index() < w.index || (v.index() == w.index && get<I>(v) < get<I>(w))</code>,
|
|
where <code>I</code> is <code>v.index()</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator>(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>w < v</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator<=(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>v.index() < w.index || (v.index() == w.index && get<I>(v) <= get<I>(w))</code>,
|
|
where <code>I</code> is <code>v.index()</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
constexpr bool operator>=(const variant<T...>& v, const variant<T...>& w);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>w <= v</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_visit">visit</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class F, class... V>
|
|
constexpr /*see below*/ visit(F&& f, V&&... v);</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Returns: </dt>
|
|
<dd>
|
|
<p><code>std::forward<F>(f)(get<I>(std::forward<V>(v))…​)</code>, where
|
|
<code>I…​</code> is <code>v.index()…​</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_swap_2">swap</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>template<class... T>
|
|
void swap(variant<T...>& v, variant<T...>& w) noexcept( /*see below*/ );</code></pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist none">
|
|
<ul class="none">
|
|
<li>
|
|
<p></p>
|
|
<div class="dlist">
|
|
<dl>
|
|
<dt class="hdlist1">Effects: </dt>
|
|
<dd>
|
|
<p>Equivalent to <code>v.swap(w)</code>.</p>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="ref_bad_variant_access">bad_variant_access</h4>
|
|
<div class="listingblock">
|
|
<div class="content">
|
|
<pre class="highlight"><code>class bad_variant_access: public std::exception
|
|
{
|
|
public:
|
|
|
|
bad_variant_access() noexcept = default;
|
|
|
|
char const * what() const noexcept
|
|
{
|
|
return "bad_variant_access";
|
|
}
|
|
};</code></pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="copyright">Copyright and License</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
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<p>This documentation is copyright 2018, 2019 Peter Dimov and is distributed under
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the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License, Version 1.0</a>.</p>
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Last updated 2019-05-12 00:15:41 +0300
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