std::is_constructible, std::is_trivially_constructible, std::is_nothrow_constructible
From cppreference.com
| Defined in header <type_traits>
|
||
| template< class T, class... Args > struct is_constructible; |
(1) | (since C++11) |
| template< class T, class... Args > struct is_trivially_constructible; |
(2) | (since C++11) |
| template< class T, class... Args > struct is_nothrow_constructible; |
(3) | (since C++11) |
1) If the expression T obj(arg1, arg2, ... argN); is well-formed, given declval<Args>()... as arguments, provides the member constant value equal true. For any other type, value is false.
2) same as 1), but the constructor expression does not call any operation that is not trivial.
3) same as 1), but the constructor expression is noexcept.
Contents |
Inherited from std::integral_constant
Member constants
| value [static] |
true if T is constructible from Args... , false otherwise (public static member constant) |
Member functions
| operator bool |
converts the object to bool, returns value (public member function) |
Member types
| Type | Definition |
value_type
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bool
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type
|
std::integral_constant<bool, value> |
[edit] Example
Run this code
#include <iostream> #include <type_traits> class Foo { int v1; double v2; public: Foo(int n) : v1(n), v2() {} Foo(int n, double f) noexcept : v1(n), v2(f) {} }; int main() { std::cout << "Foo is ...\n" << std::boolalpha << "\tTrivially-constructible from const Foo&? " << std::is_trivially_constructible<Foo, const Foo&>::value << '\n' << "\tTrivially-constructible from int? " << std::is_trivially_constructible<Foo, int>::value << '\n' << "\tConstructible from int? " << std::is_constructible<Foo, int>::value << '\n' << "\tNothrow-constructible from int? " << std::is_nothrow_constructible<Foo, int>::value << '\n' << "\tNothrow-constructible from int and double? " << std::is_nothrow_constructible<Foo, int, double>::value << '\n'; }
Output:
Foo is ...
Trivially-constructible from const Foo&? true
Trivially-constructible from int? false
Constructible from int? true
Nothrow-constructible from int? false
Nothrow-constructible from int and double? true[edit] See also
| checks if a type has a default constructor (class template) | |
| (C++11)(C++11)(C++11) |
checks if a type has a copy constructor (class template) |
| (C++11)(C++11)(C++11) |
checks if a type has a move constructor (class template) |
| (C++11) |
checks if the specified type supports uses-allocator construction (class template) |