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template<class ValueType,class...Args> std::decay_t<ValueType>& emplace( Args&&...args); | (1) | (since C++17) |
template<class ValueType,class U,class...Args> std::decay_t<ValueType>& emplace(std::initializer_list<U> il, Args&&...args); | (2) | (since C++17) |
Changes the contained object to one of typestd::decay_t<ValueType> constructed from the arguments.
First destroys the current contained object (if any) byreset(), then:
Contents |
| ValueType | - | contained value type |
| Type requirements | ||
-std::decay_t<ValueType> must meet the requirements ofCopyConstructible. | ||
A reference to the new contained object.
Throws any exception thrown byT's constructor. If an exception is thrown, the previously contained object (if any) has been destroyed, and*this does not contain a value.
#include <algorithm>#include <any>#include <iostream>#include <string>#include <vector> class Star{std::string name;int id; public: Star(std::string name,int id): name{name}, id{id}{std::cout<<"Star::Star(string, int)\n";} void print()const{std::cout<<"Star{\""<< name<<"\" : "<< id<<"};\n";}}; int main(){std::any celestial;// (1) emplace(Args&&... args); celestial.emplace<Star>("Procyon",2943);constauto* star=std::any_cast<Star>(&celestial); star->print(); std::any av;// (2) emplace(std::initializer_list<U> il, Args&&... args); av.emplace<std::vector<char>>({'C','+','+','1','7'}/* no args */);std::cout<< av.type().name()<<'\n';constauto* va=std::any_cast<std::vector<char>>(&av);std::for_each(va->cbegin(), va->cend(),[](charconst& c){std::cout<< c;});std::cout<<'\n';}
Possible output:
Star::Star(string, int)Star{"Procyon" : 2943};St6vectorIcSaIcEEC++17 constructs anany object(public member function)[edit] | |
| destroys contained object (public member function)[edit] |
