std::is_constructible, std::is_trivially_constructible, std::is_nothrow_constructible
From cppreference.com
Defined in header
<type_traits>
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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. Otherwise, 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]
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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) |
operator()
(C++14)
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returns value (public member function) |
Member types
Type | Definition |
value_type
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bool
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type
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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) |
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(C++11)(C++11)(C++11)
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checks if a type has a copy constructor (class template) |
(C++11)(C++11)(C++11)
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checks if a type has a move constructor (class template) |
(C++11)
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checks if the specified type supports uses-allocator construction (class template) |
(library fundamentals TS)
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variable template alias of std::is_constructible::value (variable template) |
(library fundamentals TS)
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variable template alias of std::is_trivially_constructible::value (variable template) |
(library fundamentals TS)
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variable template alias of std::is_nothrow_constructible::value (variable template) |