[#bsl-variant-emplace-03]
= xref:bsl.adoc[bsl]::xref:bsl/variant.adoc[variant]::emplace
:relfileprefix: ../../
:mrdocs:

`emplace` overloads

== Synopses

Declared in `<bslstl_variant.h>`

Create an object of alternative (template parameter) `t_TYPE` in place, direct‐initialized from the specified `args`, destroying any previously contained value first. Return a reference to the newly created `t_TYPE` object. If `t_TYPE` is allocator‐aware, it uses the allocator specified upon the construction of this `variant` object to supply memory; passing an allocator argument to this method results in two allocators being passed to the alternative constructor, resulting in a likely compilation error. If the constructor of `t_TYPE` exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if `t_TYPE` designates a unique alternative and is constructible from `args`. For simplicity of implementation, this method differs from the standard in the following way: * `constexpr` is not implemented


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_TYPE,
    class... t_ARGS>
requires BSLSTL_VARIANT_HAS_UNIQUE_TYPE(t_TYPE) &&
                  std::is_constructible<t_TYPE, t_ARGS...>::value
t_TYPE&
xref:bsl/variant/emplace-06.adoc[emplace](t_ARGS&&... args);
----

[.small]#xref:bsl/variant/emplace-06.adoc[_» more..._]#

Create the alternative with index (template parameter) `t_INDEX` in place, direct‐initialized from the specified `args`, destroying any previously contained value first. Return a reference to the newly created contained value. If the alternative is allocator‐aware, it uses the allocator specified upon the construction of this `variant` object to supply memory; passing an allocator argument to this method results in two allocators being passed to the alternative constructor, resulting in a likely compilation error. If the alternative constructor exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if `t_INDEX` is a valid alternative index and the designated alternative is constructible from `args`. For simplicity of implementation, this method differs from the standard in the following way: * `constexpr` is not implemented


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    std::size_t t_INDEX,
    class... t_ARGS>
requires (t_INDEX < 1 + sizeof...(t_TAIL)) &&
                  std::is_constructible<BSLSTL_VARIANT_TYPE_AT_INDEX(t_INDEX),
                                        t_ARGS...>::value
variant_alternative<t_INDEX, variant<t_HEAD, t_TAIL...>>::type&
xref:bsl/variant/emplace-02.adoc[emplace](t_ARGS&&... args);
----

[.small]#xref:bsl/variant/emplace-02.adoc[_» more..._]#

Create an object of alternative (template parameter) `t_TYPE` in place, direct‐initialized from the specified `il` and `args`, destroying any previously contained value first. Return a reference to the newly created `t_TYPE` object. If `t_TYPE` is allocator‐aware, it uses the allocator specified upon the construction of this `variant` object to supply memory; passing an allocator argument to this method results in two allocators being passed to the alternative constructor, resulting in a likely compilation error. If the constructor of `t_TYPE` exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if `t_TYPE` designates a unique alternative and is constructible from `il` and `args`. For simplicity of implementation, this method differs from the standard in the following way: * `constexpr` is not implemented


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_TYPE,
    class INIT_LIST_TYPE,
    class... t_ARGS>
requires BSLSTL_VARIANT_HAS_UNIQUE_TYPE(t_TYPE) &&
                  std::is_constructible<t_TYPE,
                                        std::initializer_list<INIT_LIST_TYPE>&,
                                        t_ARGS...>::value
t_TYPE&
xref:bsl/variant/emplace-04.adoc[emplace](
    std::initializer_list<INIT_LIST_TYPE> il,
    t_ARGS&&... args);
----

[.small]#xref:bsl/variant/emplace-04.adoc[_» more..._]#

Create the alternative with index (template parameter) `t_INDEX` in place, direct‐initialized from the specified `il` and args', destroying any previously contained value first. Return a reference to the newly created contained value. If the alternative is allocator‐aware, it uses the allocator specified upon the construction of this `variant` object to supply memory; passing an allocator argument to this method results in two allocators being passed to the alternative constructor, resulting in a likely compilation error. If the alternative constructor exits via an exception, this object may be left in the valueless by exception state. This method participates in overload resolution only if `t_INDEX` is a valid alternative index and the designated alternative is constructible from `il` and `args`. For simplicity of implementation, this method differs from the standard in the following way: * `constexpr` is not implemented


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    std::size_t t_INDEX,
    class INIT_LIST_TYPE,
    class... t_ARGS>
requires (t_INDEX < 1 + sizeof...(t_TAIL)) &&
                  std::is_constructible<BSLSTL_VARIANT_TYPE_AT_INDEX(t_INDEX),
                                        std::initializer_list<INIT_LIST_TYPE>&,
                                        t_ARGS...>::value
variant_alternative<t_INDEX, variant<t_HEAD, t_TAIL...>>::type&
xref:bsl/variant/emplace-01.adoc[emplace](
    std::initializer_list<INIT_LIST_TYPE> il,
    t_ARGS&&... args);
----

[.small]#xref:bsl/variant/emplace-01.adoc[_» more..._]#


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