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This commit is contained in:
Simon Brand
2017-10-21 19:04:41 +01:00
parent ff1b9af0bd
commit dcfccd46d8
3 changed files with 1096 additions and 1029 deletions
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20
CMakeLists.txt
View File

@@ -1,9 +1,9 @@
cmake_minimum_required(VERSION 3.0)
project(cmake_test)
project(optional)
# Prepare "Catch" library for other executables
set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
set(CATCH_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/test)
add_library(Catch INTERFACE)
target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
@@ -19,5 +19,19 @@ set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/tests/main.cpp
${CMAKE_CURRENT_SOURCE_DIR}/tests/nullopt.cpp)
add_executable(tests ${TEST_SOURCES})
target_link_libraries(tests Catch)
add_library(optional INTERFACE)
target_sources(optional INTERFACE ${CMAKE_SOURCE_DIR}/optional.hpp)
target_include_directories(optional INTERFACE ${CMAKE_SOURCE_DIR})
target_link_libraries(tests Catch optional)
set_property(TARGET tests PROPERTY CXX_STANDARD 14)
find_package(standardese REQUIRED) # find standardese after installation
# generates a custom target that will run standardese to generate the documentation
standardese_generate(optional
INCLUDE_DIRECTORY .
CONFIG ${CMAKE_SOURCE_DIR}/standardese.config
INPUT optional.hpp)

665
docs/index.md
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@@ -14,6 +14,9 @@
class <a href='doc_optional.md#optional.hpp'>bad_optional_access</a>;
template &lt;class T&gt;
class <a href='doc_optional.md#tl::optional-T-'>optional</a>;
template &lt;class T, class U&gt;
constexpr bool <a href='doc_optional.md#tl::operator==(constoptional-T-&,constoptional-U-&)'>operator==</a>(const <a href='doc_optional.md#tl::optional-T-'>optional&lt;T&gt;</a>&amp; lhs, const <a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);
template &lt;class T, class U&gt;
@@ -92,12 +95,6 @@
namespace <a href='doc_optional.md#optional.hpp'>std</a>
{
}
namespace <a href='doc_optional.md#optional.hpp'>tl</a>
{
template &lt;class T&gt;
class <a href='doc_optional.md#tl::optional-T-'>optional</a>;
}</code></pre>
## Class `tl::monostate`<a id="tl::monostate"></a>
@@ -106,7 +103,7 @@ namespace <a href='doc_optional.md#optional.hpp'>tl</a>
{
};</code></pre>
Represents an optional with no data; essentially a bool
Used to represent an optional with no data; essentially a bool
## Struct `tl::in_place_t`<a id="tl::in_place_t"></a>
@@ -146,6 +143,318 @@ Represents an empty optional
void foo (tl::optional<int>);
foo(tl::nullopt); //pass an empty optional
## Class template `tl::optional`<a id="tl::optional-T-"></a>
<pre><code class="language-cpp">template &lt;class T&gt;
class optional
{
public:
template &lt;class F&gt; constexpr auto and_then(F &amp;&amp;f);
template &lt;class F&gt; constexpr auto and_then(F &amp;&amp;f) const;
template &lt;class F&gt; auto map(F &amp;&amp;f);
template &lt;class F&gt; auto map(F &amp;&amp;f) const;
template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f);
template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) const;
template &lt;class F, class U&gt; U map_or(F &amp;&amp;f, U &amp;&amp;u);
template &lt;class F, class U&gt; U map_or(F &amp;&amp;f, U &amp;&amp;u) const;
template &lt;class F, class U&gt; U map_or_else(F &amp;&amp;f, U &amp;&amp;u);
template &lt;class F, class U&gt; U map_or_else(F &amp;&amp;f, U &amp;&amp;u) const;
using <a href='doc_optional.md#tl::optional-T-'>value_type</a> = T;
constexpr <a href='doc_optional.md#tl::optional-T-::optional()'>optional</a>() noexcept = default;
constexpr <a href='doc_optional.md#tl::optional-T-::optional()'>optional</a>(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;
constexpr <a href='doc_optional.md#tl::optional-T-::optional(constoptional-T-&)'>optional</a>(const <a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; rhs);
constexpr <a href='doc_optional.md#tl::optional-T-::optional(optional-T-&&)'>optional</a>(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_constructible&lt;T&gt;::value);
template &lt;class... Args&gt; constexpr explicit optional(in_place_t, Args&amp;&amp;... args);
template &lt;class U, class... Args&gt;
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);
template &lt;class U&gt; optional(const optional&lt;U&gt; &amp;rhs);
template &lt;class U&gt; optional(optional&lt;U&gt; &amp;&amp;rhs);
<a href='doc_optional.md#tl::optional-T-::~optional()'>~optional</a>() = default;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-::operator=(tl::nullopt_t)'>operator=</a>(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-::operator=(constoptional-T-&)'>operator=</a>(const <a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; rhs);
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-::operator=(optional-T-&&)'>operator=</a>(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_assignable&lt;T&gt;::value&amp;&amp;std::is_nothrow_move_constructible&lt;T&gt;::value);
optional &amp;operator=(U &amp;&amp;u);
optional &amp;operator=(const optional&lt;U&gt; &amp; rhs);
optional &amp;operator=(optional&lt;U&gt; &amp;&amp; rhs);
template &lt;class ... Args&gt;
T&amp; <a href='doc_optional.md#tl::optional-T-::emplace(Args&&...)'>emplace</a>(Args&amp;&amp;... args);
template &lt;class U, class... Args&gt;
T&amp; emplace(std::initializer_list&lt;U&gt; il, Args &amp;&amp;... args);
void <a href='doc_optional.md#tl::optional-T-::swap(optional-T-&)'>swap</a>(<a href='doc_optional.md#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);
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.md#tl::optional-T-::has_value()const'>has_value</a>() const noexcept;
constexpr <a href='doc_optional.md#tl::optional-T-::has_value()const'>operator bool</a>() const noexcept;
constexpr T &amp;value();
constexpr const T &amp;value() const;
template &lt;class U&gt;
constexpr T <a href='doc_optional.md#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.md#tl::optional-T-::value_or(U&&)const&'>value_or</a>(U&amp;&amp; u) &amp;&amp;;
void <a href='doc_optional.md#tl::optional-T-::reset()'>reset</a>() noexcept;
};</code></pre>
An optional object is an object that contains the storage for another object and manages the lifetime of this contained object, if any. The contained object may be initialized after the optional object has been initialized, and may be destroyed before the optional object has been destroyed. The initialization state of the contained object is tracked by the optional object.
### Function template `tl::optional::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);
(2) template &lt;class F&gt; constexpr auto and_then(F &amp;&amp;f) const;</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::map`<a id="tl::optional-T-::map(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt; auto map(F &amp;&amp;f);
(2) template &lt;class F&gt; auto map(F &amp;&amp;f) const;</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::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);
(2) template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) const;</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::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);
(2) template &lt;class F, class U&gt; U map_or(F &amp;&amp;f, U &amp;&amp;u) const;</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::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; U map_or_else(F &amp;&amp;f, U &amp;&amp;u);
(2) template &lt;class F, class U&gt; U map_or_else(F &amp;&amp;f, U &amp;&amp;u) const;</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.
### Default constructor `tl::optional::optional`<a id="tl::optional-T-::optional()"></a>
<pre><code class="language-cpp">(1) constexpr optional() noexcept = default;
(2) constexpr optional(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;</code></pre>
Constructs an optional that does not contain a value.
### 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.md#tl::optional-T-'>optional</a>&amp; rhs);</code></pre>
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>
<pre><code class="language-cpp">constexpr optional(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_constructible&lt;T&gt;::value);</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::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 optional(in_place_t, Args&amp;&amp;... args);
(2) template &lt;class U, class... Args&gt;
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.
### 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>
Constructs the stored value with `u`.
### Function template `tl::optional::optional`<a id="tl::optional-T-::optional(constoptional-U-&)"></a>
<pre><code class="language-cpp">template &lt;class U&gt; optional(const optional&lt;U&gt; &amp;rhs);</code></pre>
Converting copy constructor.
### Function template `tl::optional::optional`<a id="tl::optional-T-::optional(optional-U-&&)"></a>
<pre><code class="language-cpp">template &lt;class U&gt; optional(optional&lt;U&gt; &amp;&amp;rhs);</code></pre>
Converting move constructor.
### Destructor `tl::optional::~optional`<a id="tl::optional-T-::~optional()"></a>
<pre><code class="language-cpp">~optional() = default;</code></pre>
Destructor.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(tl::nullopt_t)"></a>
<pre><code class="language-cpp"><a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; operator=(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;</code></pre>
Assignment to empty.
Destroys the current value if there is one.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(constoptional-T-&)"></a>
<pre><code class="language-cpp"><a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; operator=(const <a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; rhs);</code></pre>
Copy assignment.
Copies the value from `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(optional-T-&&)"></a>
<pre><code class="language-cpp"><a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; operator=(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_assignable&lt;T&gt;::value&amp;&amp;std::is_nothrow_move_constructible&lt;T&gt;::value);</code></pre>
Move assignment.
Moves the value from `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(U&&)"></a>
<pre><code class="language-cpp">optional &amp;operator=(U &amp;&amp;u);</code></pre>
Assigns the stored value from `u`, destroying the old value if there was one.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(constoptional-U-&)"></a>
<pre><code class="language-cpp">optional &amp;operator=(const optional&lt;U&gt; &amp; rhs);</code></pre>
Converting copy assignment operator.
Copies the value from `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Assignment operator `tl::optional::operator=`<a id="tl::optional-T-::operator=(optional-U-&&)"></a>
<pre><code class="language-cpp">optional &amp;operator=(optional&lt;U&gt; &amp;&amp; rhs);</code></pre>
Converting move assignment operator.
Moves the value from `rhs` if there is one. Otherwise resets the stored value in `*this`.
### Function template `tl::optional::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);
(2) template &lt;class U, class... Args&gt;
T&amp; emplace(std::initializer_list&lt;U&gt; il, Args &amp;&amp;... args);</code></pre>
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>
<pre><code class="language-cpp">void swap(<a href='doc_optional.md#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);</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::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::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::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::value`<a id="tl::optional-T-::value()&"></a>
<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 \[bad\_optional\_access\]
### 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;
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::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
-----
## Comparison operator `tl::operator==`<a id="tl::operator==(constoptional-T-&,constoptional-U-&)"></a>
<pre><code class="language-cpp">(1) template &lt;class T, class U&gt;
@@ -255,345 +564,3 @@ 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.
-----
## Class template `tl::optional`<a id="tl::optional-T-"></a>
<pre><code class="language-cpp">template &lt;class T&gt;
class optional
{
public:
using <a href='doc_optional.md#tl::optional-T-'>value_type</a> = T;
constexpr <a href='doc_optional.md#tl::optional-T-::optional()'>optional</a>() noexcept = default;
constexpr <a href='doc_optional.md#tl::optional-T-::optional(tl::nullopt_t)'>optional</a>(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;
constexpr <a href='doc_optional.md#tl::optional-T-::optional(constoptional-T-&)'>optional</a>(const <a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; rhs);
constexpr <a href='doc_optional.md#tl::optional-T-::optional(optional-T-&&)'>optional</a>(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_constructible&lt;T&gt;::value);
template &lt;class ... Args&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional</a>('hidden', Args&amp;&amp;... args);
template &lt;class U, class ... Args&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional</a>('hidden', <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 U = T, 'hidden', 'hidden'&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional</a>(U&amp;&amp; u);
template &lt;class U = T, 'hidden', 'hidden'&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional</a>(U&amp;&amp; u);
template &lt;class U, 'hidden', 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>(const <a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);
template &lt;class U, 'hidden', 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>(const <a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);
template &lt;class U, 'hidden', 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>(<a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp;&amp; rhs);
template &lt;class U, 'hidden', 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>(<a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp;&amp; rhs);
<a href='doc_optional.md#tl::optional-T-'>~optional</a>() = default;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(const <a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; rhs);
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_assignable&lt;T&gt;::value&amp;&amp;std::is_nothrow_move_constructible&lt;T&gt;::value);
template &lt;class U = T, 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(U&amp;&amp; u);
template &lt;class U, 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(const <a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp; rhs);
template &lt;class U, 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp; <a href='doc_optional.md#tl::optional-T-'>operator=</a>(<a href='doc_optional.md#tl::optional-T-'>optional&lt;U&gt;</a>&amp;&amp; rhs);
template &lt;class ... Args&gt;
T&amp; <a href='doc_optional.md#tl::optional-T-'>emplace</a>(Args&amp;&amp;... args);
template &lt;class U, class ... Args&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-'>emplace</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);
void <a href='doc_optional.md#tl::optional-T-'>swap</a>(<a href='doc_optional.md#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);
constexpr const T* <a href='doc_optional.md#tl::optional-T-'>operator-&gt;</a>() const;
constexpr T* <a href='doc_optional.md#tl::optional-T-'>operator-&gt;</a>();
constexpr const T&amp; <a href='doc_optional.md#tl::optional-T-'>operator*</a>() const &amp;;
constexpr T&amp; <a href='doc_optional.md#tl::optional-T-'>operator*</a>() &amp;;
constexpr T&amp;&amp; <a href='doc_optional.md#tl::optional-T-'>operator*</a>() &amp;&amp;;
constexpr const T&amp;&amp; <a href='doc_optional.md#tl::optional-T-'>operator*</a>() const &amp;&amp;;
constexpr <a href='doc_optional.md#tl::optional-T-'>operator bool</a>() const noexcept;
constexpr bool <a href='doc_optional.md#tl::optional-T-'>has_value</a>() const noexcept;
constexpr const T&amp; <a href='doc_optional.md#tl::optional-T-'>value</a>() const &amp;;
constexpr T&amp; <a href='doc_optional.md#tl::optional-T-'>value</a>() &amp;;
constexpr T&amp;&amp; <a href='doc_optional.md#tl::optional-T-'>value</a>() &amp;&amp;;
constexpr const T&amp;&amp; <a href='doc_optional.md#tl::optional-T-'>value</a>() const &amp;&amp;;
template &lt;class U&gt;
constexpr T <a href='doc_optional.md#tl::optional-T-'>value_or</a>(U&amp;&amp; u) const &amp;;
template &lt;class U&gt;
constexpr T <a href='doc_optional.md#tl::optional-T-'>value_or</a>(U&amp;&amp; u) &amp;&amp;;
void <a href='doc_optional.md#tl::optional-T-'>reset</a>() noexcept;
template &lt;class F&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::and_then(F&&)&'>and_then</a>(F&amp;&amp; f) &amp;;
template &lt;class F&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::and_then(F&&)&'>and_then</a>(F&amp;&amp; f) const &amp;;
template &lt;class F&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::and_then(F&&)&&'>and_then</a>(F&amp;&amp; f) &amp;&amp;;
template &lt;class F&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::and_then(F&&)&&'>and_then</a>(F&amp;&amp; f) const &amp;&amp;;
template &lt;class F&gt; auto map(F &amp;&amp;f) &amp;;
template &lt;class F&gt; auto map(F &amp;&amp;f) const &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) &amp;;
template &lt;class F&gt; auto map(F &amp;&amp;f) &amp;;
template &lt;class F&gt; auto map(F &amp;&amp;f) const &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(F&amp;&amp; f) &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(F&amp;&amp; f) &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(F&amp;&amp; f) &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) const &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) const &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&'>map</a>(F&amp;&amp; f) const &amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(F&amp;&amp; f) const &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
constexpr 'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(F&amp;&amp; f) const &amp;&amp;;
template &lt;class F, 'hidden', 'hidden'&gt;
'hidden' <a href='doc_optional.md#tl::optional-T-::map(F&&)&&'>map</a>(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) const &amp;;
template &lt;class F, 'hidden'&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.md#tl::optional-T-::or_else(F&&)&'>or_else</a>(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;&amp;;
template &lt;class F, 'hidden'&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.md#tl::optional-T-::or_else(F&&)&&'>or_else</a>(F&amp;&amp; f) &amp;&amp;;
template &lt;class F, 'hidden'&gt;
constexpr <a href='doc_optional.md#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.md#tl::optional-T-::or_else(F&&)&'>or_else</a>(F&amp;&amp; f) const &amp;;
template &lt;class F, 'hidden'&gt;
<a href='doc_optional.md#tl::optional-T-'>optional&lt;T&gt;</a> <a href='doc_optional.md#tl::optional-T-::or_else(F&&)&&'>or_else</a>(F&amp;&amp; f) const &amp;&amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.md#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.md#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.md#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.md#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;
U <a href='doc_optional.md#tl::optional-T-::map_or_else(F&&,U&&)&'>map_or_else</a>(F&amp;&amp; f, U&amp;&amp; u) &amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.md#tl::optional-T-::map_or_else(F&&,U&&)&'>map_or_else</a>(F&amp;&amp; f, U&amp;&amp; u) const &amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.md#tl::optional-T-::map_or_else(F&&,U&&)&&'>map_or_else</a>(F&amp;&amp; f, U&amp;&amp; u) &amp;&amp;;
template &lt;class F, class U&gt;
U <a href='doc_optional.md#tl::optional-T-::map_or_else(F&&,U&&)&&'>map_or_else</a>(F&amp;&amp; f, U&amp;&amp; u) const &amp;&amp;;
};</code></pre>
An optional object is an object that contains the storage for another object and manages the lifetime of this contained object, if any. The contained object may be initialized after the optional object has been initialized, and may be destroyed before the optional object has been destroyed. The initialization state of the contained object is tracked by the optional object.
### Default constructor `tl::optional::optional`<a id="tl::optional-T-::optional()"></a>
<pre><code class="language-cpp">constexpr optional() noexcept = default;</code></pre>
Constructs an optional that does not contain a value.
### Constructor `tl::optional::optional`<a id="tl::optional-T-::optional(tl::nullopt_t)"></a>
<pre><code class="language-cpp">constexpr optional(<a href='doc_optional.md#tl::nullopt_t'>nullopt_t</a>) noexcept;</code></pre>
Constructs an optional that does not contain a value.
### 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.md#tl::optional-T-'>optional</a>&amp; rhs);</code></pre>
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>
<pre><code class="language-cpp">constexpr optional(<a href='doc_optional.md#tl::optional-T-'>optional</a>&amp;&amp; rhs) noexcept(std::is_nothrow_move_constructible&lt;T&gt;::value);</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::and_then`<a id="tl::optional-T-::and_then(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt;
constexpr 'hidden' and_then(F&amp;&amp; f) &amp;;
(2) template &lt;class F&gt;
constexpr 'hidden' and_then(F&amp;&amp; f) const &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::and_then`<a id="tl::optional-T-::and_then(F&&)&&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt;
constexpr 'hidden' and_then(F&amp;&amp; f) &amp;&amp;;
(2) template &lt;class F&gt;
constexpr 'hidden' 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), std::move(value()))` returns a `std::optional<U>` for some `U`.
*Returns*: Let `U` be the result of `std::invoke(std::forward<F>(f), std::move(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), std::move(value()))` is returned.
### Function template `tl::optional::map`<a id="tl::optional-T-::map(F&&)&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt; auto map(F &amp;&amp;f) &amp;;
(2) template &lt;class F&gt; auto map(F &amp;&amp;f) const &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::map`<a id="tl::optional-T-::map(F&&)&&"></a>
<pre><code class="language-cpp">(1) template &lt;class F&gt; auto map(F &amp;&amp;f) &amp;;
(2) template &lt;class F&gt; 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), std::move(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), std::move(value()))` and is returned.
### Function template `tl::optional::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) 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::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;&amp;;
(2) template &lt;class F&gt; optional&lt;T&gt; or_else (F &amp;&amp;f) const &amp;&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 `std::move(*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>
<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) const &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::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;&amp;;
(2) 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 `std::move(**this)` and the value is returned. Otherwise `u` is returned.
### Function template `tl::optional::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;
U map_or_else(F&amp;&amp; f, U&amp;&amp; u) &amp;;
(2) template &lt;class F, class U&gt;
U map_or_else(F&amp;&amp; f, U&amp;&amp; u) const &amp;;</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::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;
U map_or_else(F&amp;&amp; f, U&amp;&amp; u) &amp;&amp;;
(2) template &lt;class F, class U&gt;
U map_or_else(F&amp;&amp; f, U&amp;&amp; u) const &amp;&amp;;</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 `std::move(**this)` and the value is returned. Otherwise `std::forward<U>(u)()` is returned.
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