feedc0de/optional
1
0
Fork 0
forked from TartanLlama/optional
Code Pull Requests Activity

Publish docs

Browse Source
This commit is contained in:
Simon Brand
2017-12-18 10:55:36 +00:00
parent f621ca663e
commit 883df6b427
1 changed files with 405 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

435
docs/index.md
View File

@ -99,16 +99,24 @@ namespace <a href='doc_optional.html#optional.hpp'>tl</a>
constexpr bool <a href='doc_optional.html#tl::operator==(constoptional-T-&,constU&)'>operator&gt;=</a>(const U&amp; lhs, const <a href='doc_optional.html#tl::optional-T-'>optional&lt;T&gt;</a>&amp; rhs);
template &lt;class T&gt;
void swap(optional&lt;T&gt; &amp;lhs, optional&lt;T&gt;
void swap(optional&lt;T&gt; &amp;lhs, optional&lt;T&gt; &amp;rhs);
template &lt;class T&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;detail::decay_t&lt;T&gt;&gt;</a> <a href='doc_optional.html#optional.hpp'>make_optional</a>(T&amp;&amp; v);
namespace <a href='doc_optional.html#optional.hpp'>detail</a>
{
struct <a href='doc_optional.html#optional.hpp'>i_am_secret</a>;
}
template &lt;class T = detail::i_am_secret, class U, class Ret = detail::conditional_t&lt;std::is_same&lt;T, detail::i_am_secret&gt;::value, detail::decay_t&lt;U&gt;, T&gt;&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;Ret&gt;</a> <a href='doc_optional.html#optional.hpp'>make_optional</a>(U&amp;&amp; v);
template &lt;class T, class ... Args&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.html#optional.hpp'>make_optional</a>(Args&amp;&amp;... args);
template &lt;class T, class U, class ... Args&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.html#optional.hpp'>make_optional</a>(<a href='http://en.cppreference.com/mwiki/index.php?title=Special%3ASearch&search=std::initializer_list%3cU%3e'>std::initializer_list&lt;U&gt;</a> il, Args&amp;&amp;... args);
template &lt;class T&gt;
class <a href='doc_optional.html#tl::optional-T&-'>optional&lt;T&amp;&gt;</a>;
}
namespace <a href='doc_optional.html#optional.hpp'>std</a>
@ -229,9 +237,9 @@ public:
constexpr <a href='doc_optional.html#tl::optional-T-::optional(optional-T-&&)'>optional</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) = default;
template &lt;class... Args&gt; constexpr explicit
template &lt;class... Args&gt; constexpr explicit optional(in_place_t, Args&amp;&amp;... args);
template &lt;class U, class... Args&gt;
constexpr explicit
constexpr explicit optional(in_place_t, std::initializer_list&lt;U&gt;&amp;, Args&amp;&amp;... args);
template &lt;class U=T&gt; constexpr optional(U &amp;&amp;u);
@ -255,9 +263,8 @@ public:
template &lt;class ... Args&gt;
T&amp; <a href='doc_optional.html#tl::optional-T-::emplace(Args&&...)'>emplace</a>(Args&amp;&amp;... args);
template &lt;class U, class... Args&gt;
T&amp;
T&amp; emplace(std::initializer_list&lt;U&gt; il, Args &amp;&amp;... args);
void <a href='doc_optional.html#tl::optional-T-::swap(optional-T-&)'>swap</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) noexcept(std::is_nothrow_move_constructible&lt;T&gt;::value&amp;&amp;detail::is_nothrow_swappable&lt;T&gt;::value);
@ -270,7 +277,7 @@ public:
constexpr bool <a href='doc_optional.html#tl::optional-T-::has_value()const'>has_value</a>() const noexcept;
constexpr <a href='doc_optional.html#tl::optional-T-::has_value()const'>operator bool</a>() const noexcept;
constexpr T&amp; <a href='doc_optional.html#tl::optional-T-::value()&'>value</a>() &amp;;
constexpr T &amp;value();
constexpr const T &amp;value() const;
template &lt;class U&gt;
@ -323,7 +330,9 @@ Carries out some operation on the stored object if there is one.
Calls `f` if the optional is empty
*Requires*: `std::invoke_result_t<F>` must be void or convertible to `optional<T>`. \\effects If `*this` has a value, returns `*this`. Otherwise, if `f` returns `void`, calls `std::forward<F>(f)` and returns `std::nullopt`. Otherwise, returns `std::forward<F>(f)()`.
*Requires*: `std::invoke_result_t<F>` must be void or convertible to `optional<T>`.
*Effects*: If `*this` has a value, returns `*this`. Otherwise, if `f` returns `void`, calls `std::forward<F>(f)` and returns `std::nullopt`. Otherwise, returns `std::forward<F>(f)()`.
### Function template `tl::optional::map_or`<a id="tl::optional-T-::map_or(F&&,U&&)&"></a>
@ -408,7 +417,7 @@ Takes the value out of the optional, leaving it empty
Constructs an optional that does not contain a value.
### Constructor `tl::optional::optional`<a id="tl::optional-T-::optional(constoptional-T-&)"></a>
### Copy constructor `tl::optional::optional`<a id="tl::optional-T-::optional(constoptional-T-&)"></a>
<pre><code class="language-cpp">constexpr optional(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) = default;</code></pre>
@ -416,7 +425,7 @@ Copy constructor
If `rhs` contains a value, the stored value is direct-initialized with it. Otherwise, the constructed optional is empty.
### Constructor `tl::optional::optional`<a id="tl::optional-T-::optional(optional-T-&&)"></a>
### Move constructor `tl::optional::optional`<a id="tl::optional-T-::optional(optional-T-&&)"></a>
<pre><code class="language-cpp">constexpr optional(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) = default;</code></pre>
@ -426,15 +435,13 @@ If `rhs` contains a value, the stored value is direct-initialized with it. Other
### Function template `tl::optional::optional`<a id="tl::optional-T-::optional(detail::enable_if_t-std::is_constructible-T,Args...-::value,in_place_t-,Args&&...)"></a>
<pre><code class="language-cpp">(1) template &lt;class... Args&gt; constexpr explicit
<pre><code class="language-cpp">(1) template &lt;class... Args&gt; constexpr explicit optional(in_place_t, Args&amp;&amp;... args);
(2) template &lt;class U, class... Args&gt;
constexpr explicit</code></pre>
constexpr explicit optional(in_place_t, std::initializer_list&lt;U&gt;&amp;, Args&amp;&amp;... args);</code></pre>
Constructs the stored value in-place using the given arguments.
optional(in\_place\_t, Args&&... args);
### Function template `tl::optional::optional`<a id="tl::optional-T-::optional(U&&)"></a>
<pre><code class="language-cpp">template &lt;class U=T&gt; constexpr optional(U &amp;&amp;u);</code></pre>
@ -507,17 +514,13 @@ Moves the value from `rhs` if there is one. Otherwise resets the stored value in
### Function template `tl::optional::emplace`<a id="tl::optional-T-::emplace(Args&&...)"></a>
<pre><code class="language-cpp">template &lt;class ... Args&gt;
T&amp; emplace(Args&amp;&amp;... args);</code></pre>
<pre><code class="language-cpp">(1) template &lt;class ... Args&gt;
T&amp; emplace(Args&amp;&amp;... args);
Constructs the value in-place, destroying the current one if there is one. \\group emplace
(2) template &lt;class U, class... Args&gt;
T&amp; emplace(std::initializer_list&lt;U&gt; il, Args &amp;&amp;... args);</code></pre>
### Function template `tl::optional::emplace`<a id="tl::optional-T-::emplace(std::initializer_list-U-,Args&&...)"></a>
<pre><code class="language-cpp">(1) template &lt;class U, class... Args&gt;
T&amp;</code></pre>
emplace(std::initializer\_list\<U\> il, Args &&... args);
Constructs the value in-place, destroying the current one if there is one.
### Function `tl::optional::swap`<a id="tl::optional-T-::swap(optional-T-&)"></a>
@ -557,14 +560,12 @@ If neither optionals have a value, nothing happens. If both have a value, the va
### Function `tl::optional::value`<a id="tl::optional-T-::value()&"></a>
<pre><code class="language-cpp">(1) constexpr T&amp; value() &amp;;
<pre><code class="language-cpp">(1) constexpr T &amp;value();
(2) constexpr const T &amp;value() const;</code></pre>
*Returns*: the contained value if there is one, otherwise throws \[bad\_optional\_access\]
synopsis constexpr T \&value();
### Function template `tl::optional::value_or`<a id="tl::optional-T-::value_or(U&&)const&"></a>
<pre><code class="language-cpp">(1) template &lt;class U&gt;
@ -691,11 +692,385 @@ Compares the optional with a value.
If the optional has a value, it is compared with the other value using `T`s relational operators. Otherwise, the optional is considered less than the value.
## Function template `tl::swap`<a id="tl::swap(optional-T-&,optional-T-&)"></a>
## Class template `tl::optional<T&>`<a id="tl::optional-T&-"></a>
<pre><code class="language-cpp">template &lt;class T&gt;
void swap(optional&lt;T&gt; &amp;lhs, optional&lt;T&gt;</code></pre>
class optional&lt;T&amp;&gt;
{
public:
template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) &amp;;
template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) &amp;&amp;;
template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) const &amp;;
template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) const &amp;&amp;;
template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) &amp;;
template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) &amp;&amp;;
template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) const&amp;;
template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) const&amp;&amp;;
template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) &amp;;
template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) &amp;&amp;;
template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) const &amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.html#tl::optional-T&-::map_or(F&&,U&&)&'>map_or</a>(F&amp;&amp; f, U&amp;&amp; u) &amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.html#tl::optional-T&-::map_or(F&&,U&&)&'>map_or</a>(F&amp;&amp; f, U&amp;&amp; u) &amp;&amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.html#tl::optional-T&-::map_or(F&&,U&&)&'>map_or</a>(F&amp;&amp; f, U&amp;&amp; u) const &amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.html#tl::optional-T&-::map_or(F&&,U&&)&'>map_or</a>(F&amp;&amp; f, U&amp;&amp; u) const &amp;&amp;;
template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u) &amp;;
template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)
template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)
template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)
template &lt;class U&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;typename std::decay&lt;U&gt;::type&gt;</a> <a href='doc_optional.html#tl::optional-T&-::conjunction(U&&)const'>conjunction</a>(U&amp;&amp; u) const;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) &amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) const &amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) &amp;&amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) const &amp;&amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) &amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) const &amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) &amp;&amp;;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::disjunction(constoptional&)&'>disjunction</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) const &amp;&amp;;
<a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::take()&'>take</a>() &amp;;
<a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::take()&'>take</a>() const &amp;;
<a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::take()&'>take</a>() &amp;&amp;;
<a href='doc_optional.html#tl::optional-T-'>optional</a> <a href='doc_optional.html#tl::optional-T&-::take()&'>take</a>() const &amp;&amp;;
using <a href='doc_optional.html#tl::optional-T&-'>value_type</a> = T&amp;;
constexpr <a href='doc_optional.html#tl::optional-T&-::optional()'>optional</a>() noexcept;
constexpr <a href='doc_optional.html#tl::optional-T&-::optional()'>optional</a>(<a href='doc_optional.html#tl::nullopt_t'>nullopt_t</a>) noexcept;
constexpr <a href='doc_optional.html#tl::optional-T&-::optional(constoptional&)'>optional</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) noexcept = default;
constexpr <a href='doc_optional.html#tl::optional-T&-::optional(optional&&)'>optional</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) = default;
template &lt;class U=T&gt; constexpr optional(U &amp;&amp;u);
<a href='doc_optional.html#tl::optional-T&-::~optional()'>~optional</a>() = default;
<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.html#tl::optional-T&-::operator=(tl::nullopt_t)'>operator=</a>(<a href='doc_optional.html#tl::nullopt_t'>nullopt_t</a>) noexcept;
<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.html#tl::optional-T&-::operator=(constoptional&)'>operator=</a>(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) = default;
optional &amp;operator=(U &amp;&amp;u);
template &lt;class U&gt;
<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.html#tl::optional-T&-::operator=(constoptional-U-&)'>operator=</a>(const <a href='doc_optional.html#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);
template &lt;class ... Args&gt;
T&amp; <a href='doc_optional.html#tl::optional-T&-::emplace(Args&&...)'>emplace</a>(Args&amp;&amp;... args) noexcept;
void <a href='doc_optional.html#tl::optional-T&-::swap(optional&)'>swap</a>(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) noexcept;
constexpr const T *operator-&gt;() const;
constexpr T *operator-&gt;();
constexpr T &amp;operator*();
constexpr const T &amp;operator*() const;
constexpr bool <a href='doc_optional.html#tl::optional-T&-::has_value()const'>has_value</a>() const noexcept;
constexpr <a href='doc_optional.html#tl::optional-T&-::has_value()const'>operator bool</a>() const noexcept;
constexpr T&amp; <a href='doc_optional.html#tl::optional-T&-::value()&'>value</a>() &amp;;
constexpr const T &amp;value() const;
template &lt;class U&gt;
constexpr T <a href='doc_optional.html#tl::optional-T&-::value_or(U&&)const&'>value_or</a>(U&amp;&amp; u) const &amp;;
template &lt;class U&gt;
constexpr T <a href='doc_optional.html#tl::optional-T&-::value_or(U&&)const&'>value_or</a>(U&amp;&amp; u) &amp;&amp;;
void <a href='doc_optional.html#tl::optional-T&-::reset()'>reset</a>() noexcept;
};</code></pre>
\&rhs);
Specialization for when `T` is a reference. `optional<T&>` acts similarly to a `T*`, but provides more operations and shows intent more clearly.
*Examples*:
int i = 42;
tl::optional<int&> o = i;
*o == 42; //true
i = 12;
*o = 12; //true
&*o == &i; //true
Assignment has rebind semantics rather than assign-through semantics:
int j = 8;
o = j;
&*o == &j; //true
### Function template `tl::optional<T&>::and_then`<a id="tl::optional-T&-::and_then(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) &amp;;
(2) template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) &amp;&amp;;
(3) template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) const &amp;;
(4) template &lt;class F&gt;
constexpr auto and_then(F &amp;&amp;f) const &amp;&amp;;</code></pre>
Carries out some operation which returns an optional on the stored object if there is one. \\requires `std::invoke(std::forward<F>(f), value())` returns a `std::optional<U>` for some `U`. \\returns Let `U` be the result of `std::invoke(std::forward<F>(f), value())`. Returns a `std::optional<U>`. The return value is empty if `*this` is empty, otherwise the return value of `std::invoke(std::forward<F>(f), value())` is returned.
### Function template `tl::optional<T&>::map`<a id="tl::optional-T&-::map(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) &amp;;
(2) template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) &amp;&amp;;
(3) template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) const&amp;;
(4) template &lt;class F&gt; constexpr auto map(F &amp;&amp;f) const&amp;&amp;;</code></pre>
Carries out some operation on the stored object if there is one.
*Returns*: Let `U` be the result of `std::invoke(std::forward<F>(f), value())`. Returns a `std::optional<U>`. The return value is empty if `*this` is empty, otherwise an `optional<U>` is constructed from the return value of `std::invoke(std::forward<F>(f), value())` and is returned.
### Function template `tl::optional<T&>::or_else`<a id="tl::optional-T&-::or_else(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) &amp;;
(2) template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) &amp;&amp;;
(3) template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) const &amp;;</code></pre>
Calls `f` if the optional is empty
*Requires*: `std::invoke_result_t<F>` must be void or convertible to `optional<T>`. \\effects If `*this` has a value, returns `*this`. Otherwise, if `f` returns `void`, calls `std::forward<F>(f)` and returns `std::nullopt`. Otherwise, returns `std::forward<F>(f)()`.
### Function template `tl::optional<T&>::map_or`<a id="tl::optional-T&-::map_or(F&&,U&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F, class U&gt;
U map_or(F&amp;&amp; f, U&amp;&amp; u) &amp;;
(2) template &lt;class F, class U&gt;
U map_or(F&amp;&amp; f, U&amp;&amp; u) &amp;&amp;;
(3) template &lt;class F, class U&gt;
U map_or(F&amp;&amp; f, U&amp;&amp; u) const &amp;;
(4) template &lt;class F, class U&gt;
U map_or(F&amp;&amp; f, U&amp;&amp; u) const &amp;&amp;;</code></pre>
Maps the stored value with `f` if there is one, otherwise returns `u`.
If there is a value stored, then `f` is called with `**this` and the value is returned. Otherwise `u` is returned.
### Function template `tl::optional<T&>::map_or_else`<a id="tl::optional-T&-::map_or_else(F&&,U&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u) &amp;;
(2) template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)
(3) template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)
(4) template &lt;class F, class U&gt;
auto map_or_else(F &amp;&amp;f, U &amp;&amp;u)</code></pre>
Maps the stored value with `f` if there is one, otherwise calls `u` and returns the result.
If there is a value stored, then `f` is called with `**this` and the value is returned. Otherwise `std::forward<U>(u)()` is returned.
### Function template `tl::optional<T&>::conjunction`<a id="tl::optional-T&-::conjunction(U&&)const"></a>
<pre><code class="language-cpp">template &lt;class U&gt;
constexpr <a href='doc_optional.html#tl::optional-T-'>optional&lt;typename std::decay&lt;U&gt;::type&gt;</a> conjunction(U&amp;&amp; u) const;</code></pre>
*Returns*: `u` if `*this` has a value, otherwise an empty optional.
### Function `tl::optional<T&>::disjunction`<a id="tl::optional-T&-::disjunction(constoptional&)&"></a>
<pre><code class="language-cpp">(1) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) &amp;;
(2) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) const &amp;;
(3) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) &amp;&amp;;
(4) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) const &amp;&amp;;
(5) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) &amp;;
(6) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) const &amp;;
(7) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) &amp;&amp;;
(8) constexpr <a href='doc_optional.html#tl::optional-T-'>optional</a> disjunction(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) const &amp;&amp;;</code></pre>
*Returns*: `rhs` if `*this` is empty, otherwise the current value.
### Function `tl::optional<T&>::take`<a id="tl::optional-T&-::take()&"></a>
<pre><code class="language-cpp">(1) <a href='doc_optional.html#tl::optional-T-'>optional</a> take() &amp;;
(2) <a href='doc_optional.html#tl::optional-T-'>optional</a> take() const &amp;;
(3) <a href='doc_optional.html#tl::optional-T-'>optional</a> take() &amp;&amp;;
(4) <a href='doc_optional.html#tl::optional-T-'>optional</a> take() const &amp;&amp;;</code></pre>
Takes the value out of the optional, leaving it empty
### Default constructor `tl::optional<T&>::optional`<a id="tl::optional-T&-::optional()"></a>
<pre><code class="language-cpp">(1) constexpr optional() noexcept;
(2) constexpr optional(<a href='doc_optional.html#tl::nullopt_t'>nullopt_t</a>) noexcept;</code></pre>
Constructs an optional that does not contain a value.
### Copy constructor `tl::optional<T&>::optional`<a id="tl::optional-T&-::optional(constoptional&)"></a>
<pre><code class="language-cpp">constexpr optional(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) noexcept = default;</code></pre>
Copy constructor
If `rhs` contains a value, the stored value is direct-initialized with it. Otherwise, the constructed optional is empty.
### Move constructor `tl::optional<T&>::optional`<a id="tl::optional-T&-::optional(optional&&)"></a>
<pre><code class="language-cpp">constexpr optional(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp;&amp; rhs) = default;</code></pre>
Move constructor
If `rhs` contains a value, the stored value is direct-initialized with it. Otherwise, the constructed optional is empty.
### Function template `tl::optional<T&>::optional`<a id="tl::optional-T&-::optional(U&&)"></a>
<pre><code class="language-cpp">template &lt;class U=T&gt; constexpr optional(U &amp;&amp;u);</code></pre>
Constructs the stored value with `u`.
### Destructor `tl::optional<T&>::~optional`<a id="tl::optional-T&-::~optional()"></a>
<pre><code class="language-cpp">~optional() = default;</code></pre>
No-op
### Assignment operator `tl::optional<T&>::operator=`<a id="tl::optional-T&-::operator=(tl::nullopt_t)"></a>
<pre><code class="language-cpp"><a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; operator=(<a href='doc_optional.html#tl::nullopt_t'>nullopt_t</a>) noexcept;</code></pre>
Assignment to empty.
Destroys the current value if there is one.
### Copy assignment operator `tl::optional<T&>::operator=`<a id="tl::optional-T&-::operator=(constoptional&)"></a>
<pre><code class="language-cpp"><a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; operator=(const <a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) = default;</code></pre>
Copy assignment.
Rebinds this optional to the referee of `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Assignment operator `tl::optional<T&>::operator=`<a id="tl::optional-T&-::operator=(U&&)"></a>
<pre><code class="language-cpp">optional &amp;operator=(U &amp;&amp;u);</code></pre>
Rebinds this optional to `u`.
*Requires*: `U` must be an lvalue reference.
### Assignment operator `tl::optional<T&>::operator=`<a id="tl::optional-T&-::operator=(constoptional-U-&)"></a>
<pre><code class="language-cpp">template &lt;class U&gt;
<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; operator=(const <a href='doc_optional.html#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);</code></pre>
Converting copy assignment operator.
Rebinds this optional to the referee of `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Function template `tl::optional<T&>::emplace`<a id="tl::optional-T&-::emplace(Args&&...)"></a>
<pre><code class="language-cpp">(1) template &lt;class ... Args&gt;
T&amp; emplace(Args&amp;&amp;... args) noexcept;</code></pre>
Constructs the value in-place, destroying the current one if there is one.
### Function `tl::optional<T&>::swap`<a id="tl::optional-T&-::swap(optional&)"></a>
<pre><code class="language-cpp">void swap(<a href='doc_optional.html#tl::optional-T-'>optional</a>&amp; rhs) noexcept;</code></pre>
Swaps this optional with the other.
If neither optionals have a value, nothing happens. If both have a value, the values are swapped. If one has a value, it is moved to the other and the movee is left valueless.
### Operator `tl::optional<T&>::operator->`<a id="tl::optional-T&-::operator--()const"></a>
<pre><code class="language-cpp">(1) constexpr const T *operator-&gt;() const;
(2) constexpr T *operator-&gt;();</code></pre>
*Returns*: a pointer to the stored value
*Requires*: a value is stored
### Operator `tl::optional<T&>::operator*`<a id="tl::optional-T&-::operator*()&"></a>
<pre><code class="language-cpp">(1) constexpr T &amp;operator*();
(2) constexpr const T &amp;operator*() const;</code></pre>
*Returns*: the stored value
*Requires*: a value is stored
### Function `tl::optional<T&>::has_value`<a id="tl::optional-T&-::has_value()const"></a>
<pre><code class="language-cpp">(1) constexpr bool has_value() const noexcept;
(2) constexpr operator bool() const noexcept;</code></pre>
*Returns*: whether or not the optional has a value
### Function `tl::optional<T&>::value`<a id="tl::optional-T&-::value()&"></a>
<pre><code class="language-cpp">(1) constexpr T&amp; value() &amp;;
(2) constexpr const T &amp;value() const;</code></pre>
*Returns*: the contained value if there is one, otherwise throws \[bad\_optional\_access\]
synopsis constexpr T \&value();
### Function template `tl::optional<T&>::value_or`<a id="tl::optional-T&-::value_or(U&&)const&"></a>
<pre><code class="language-cpp">(1) template &lt;class U&gt;
constexpr T value_or(U&amp;&amp; u) const &amp;;
(2) template &lt;class U&gt;
constexpr T value_or(U&amp;&amp; u) &amp;&amp;;</code></pre>
*Returns*: the stored value if there is one, otherwise returns `u`
### Function `tl::optional<T&>::reset`<a id="tl::optional-T&-::reset()"></a>
<pre><code class="language-cpp">void reset() noexcept;</code></pre>
Destroys the stored value if one exists, making the optional empty
-----
-----