View source for Template:cpp/container/emplace ad

{{cpp/container/{{{1|}}}/title|emplace}}
{{cpp/container/{{{1|}}}/navbar}}
{{dcl begin}}
{{#switch:{{{1|}}}
|stack|queue=
{{dcl rev multi|since1=c++11|until1=c++17
|dcl1=
template< class... Args >
void emplace( Args&&... args );
|dcl2=
template< class... Args >
decltype(auto) emplace( Args&&... args );
}}
|<!--priority_queue=-->
{{dcl|since=c++11|
template< class... Args >
void emplace( Args&&... args );
}}
}}
{{dcl end}}
{{#vardefine:inplace note|The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element is called with exactly the same arguments as supplied to the function.}}
{{#switch:{{{1|}}}
|stack=Pushes a new element on top of the stack. {{#var:inplace note}}

Effectively calls {{c|c.emplace_back(std::forward<Args>(args)...);}}.

|queue=Pushes a new element to the end of the queue. {{#var:inplace note}}

Effectively calls {{c|c.emplace_back(std::forward<Args>(args)...);}}.

|<!--priority_queue=-->Pushes a new element to the priority queue. {{#var:inplace note}}

Effectively calls {{source|
c.emplace_back(std::forward<Args>(args)...);
std::push_heap(c.begin(), c.end(), comp);
}}
}}

===Parameters===
{{par begin}}
{{par|args|arguments to forward to the constructor of the element}}
{{par end}}

===Return value===
{{#switch:{{{1|}}}
|stack|queue=
{{rrev multi|until1=c++17
|rev1=(none)
|rev2=The value or reference, if any, returned by the above call to {{c|Container::emplace_back}}.
}}
|<!--priority_queue=-->(none)
}}

===Complexity===
{{#switch:{{{1|}}}
|stack|queue=Identical to the complexity of {{c|Container::emplace_back}}.
|<!--priority_queue=-->Logarithmic number of comparisons plus the complexity of {{c|Container::emplace_back}}.
}}

===Example===
{{#vardefine:adaptor|{{cpp/container/get header|{{{1|priority_queue}}}}}}}
{{example
|code=
#include <iostream>
#include <{{#var:adaptor}}>

{{#switch:{{{1|}}}
|stack|queue=
struct S
{
    int id;

    S(int i, double d, std::string s) : id{i}
    {
        std::cout << "S::S(" << i << ", " << d << ", \"" << s << "\");\n";
    }
};

int main()
{
    std::{{{1|}}}<S> {{#var:adaptor}};
    const S& s = {{#var:adaptor}}.emplace(42, 3.14, "C++"); // for return value C++17 required
    std::cout << "id = " << s.id << '\n';
}
|<!--priority_queue=-->
struct S
{
    int id;

    S(int i, double d, std::string s) : id{i}
    {
        std::cout << "S::S(" << i << ", " << d << ", \"" << s << "\");\n";
    }
    friend bool operator< (S const& x, S const& y) { return x.id < y.id; }
};

int main()
{
    std::priority_queue<S> {{#var:adaptor}};
    {{#var:adaptor}}.emplace(42, 3.14, "C++");
    std::cout << "id: " << {{#var:adaptor}}.top().id << '\n';
}
}}
|output=
S::S(42, 3.14, "C++")
id = 42
}}
<!---->
{{#switch:{{{1|}}}
|stack|queue=
===Defect reports===
{{dr list begin}}
{{dr list item|wg=lwg|dr=2783|std=C++17|before={{tt|emplace}} returned {{tt|reference}}, breaking compatibility with pre-C++17 containers|after=returns {{tt|decltype(auto)}}}}
{{dr list end}}
}}
<!---->
===See also===
{{dsc begin}}
{{dsc inc|cpp/container/dsc push|{{{1|}}}}}
{{dsc inc|cpp/container/dsc pop|{{{1|}}}}}
{{dsc end}}