<type_traits>

class template
<type_traits>

std::is_constructible

template <class T, class... Args> struct is_constructible;
Is constructible

Trait class that identifies whether T is a constructible type with the set of argument types specified by Arg.

For this class, a constructible type is a type that can be constructed using a particular set of arguments.

is_constructible inherits from integral_constant as being either true_type or false_type, depending on whether T is constructible with the list of arguments Args.

Template parameters

T
A complete type, or void (possible cv-qualified), or an array of unknown bound.
Args
A list of complete types (or void, possibly cv-qualified, or an array of unknown bound) representing the argument types for the constructor form, in the same order as in the constructor.
If omitted, it checks whether the type is default-constructible.

Member types

Inherited from integral_constant:
member typedefinition
value_typebool
typeeither true_type or false_type

Member constants

Inherited from integral_constant:
member constantdefinition
valueeither true or false

Member functions

Inherited from integral_constant:

Example

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// is_constructible example
#include <iostream>
#include <type_traits>

struct A { A (int,int) {}; };

int main() {
  std::cout << std::boolalpha;
  std::cout << "is_constructible:" << std::endl;
  std::cout << "int: " << std::is_constructible<int>::value << std::endl;
  std::cout << "int(float): " << std::is_constructible<int,float>::value << std::endl;
  std::cout << "int(float,float): " << std::is_constructible<int,float,float>::value << std::endl;
  std::cout << "A: " << std::is_constructible<A>::value << std::endl;
  std::cout << "A(int): " << std::is_constructible<A,int>::value << std::endl;
  std::cout << "A(int,int): " << std::is_constructible<A,int,int>::value << std::endl;
  std::cout << "A(int,int,int): " << std::is_constructible<A,int,int,int>::value << std::endl;
  return 0;
}


Output:
is_constructible:
int: true
int(float): true
int(float,float): false
A: false
A(int): false
A(int,int): true
A(int,int,int): false

See also