std::is_invocable, std::is_invocable_r, std::is_nothrow_invocable, std::is_nothrow_invocable_r

 

C++

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Metaprogramming library

Type traits
Type categories is_void (C++11) is_null_pointer (C++14)   is_array (C++11) is_pointer (C++11) is_enum (C++11) is_union (C++11) is_class (C++11) is_function (C++11) is_object (C++11) is_scalar (C++11) is_compound (C++11) is_integral (C++11) is_floating_point (C++11)   is_fundamental (C++11) is_arithmetic (C++11) is_reference (C++11) is_lvalue_reference (C++11) is_rvalue_reference (C++11) is_member_pointer (C++11) is_member_object_pointer (C++11) is_member_function_pointer (C++11) Type properties is_const (C++11) is_volatile (C++11) is_empty (C++11) is_polymorphic (C++11) is_final (C++14) is_abstract (C++11) is_aggregate (C++17) is_implicit_lifetime (C++23) is_trivial (C++11) is_trivially_copyable (C++11) is_standard_layout (C++11) is_literal_type (C++11)(until C++20*) is_pod (C++11)(deprecated in C++20) is_signed (C++11) is_unsigned (C++11) is_bounded_array (C++20) is_unbounded_array (C++20) is_scoped_enum (C++23) has_unique_object_representations (C++17) Type trait constants integral_constantbool_constanttrue_typefalse_type (C++11)(C++17)(C++11)(C++11) Metafunctions conjunction (C++17) disjunction (C++17) negation (C++17)	Supported operations is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11) is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11) is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11) is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11) is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11) is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11) has_virtual_destructor (C++11) is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17) Relationships and property queries is_same (C++11) is_base_of (C++11) is_convertibleis_nothrow_convertible (C++11)(C++20) is_layout_compatible (C++20) is_pointer_interconvertible_base_of (C++20) is_pointer_interconvertible_with_class (C++20)   is_corresponding_member (C++20) alignment_of (C++11) rank (C++11) extent (C++11) is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17) reference_constructs_from_temporary (C++23) reference_converts_from_temporary (C++23) Type modifications remove_cvremove_constremove_volatile (C++11)(C++11)(C++11) add_cvadd_constadd_volatile (C++11)(C++11)(C++11) make_signed (C++11) make_unsigned (C++11) remove_reference (C++11) add_lvalue_referenceadd_rvalue_reference (C++11)(C++11) remove_pointer (C++11) add_pointer (C++11) remove_extent (C++11) remove_all_extents (C++11) Type transformations aligned_storage (C++11)(deprecated in C++23) aligned_union (C++11)(deprecated in C++23) decay (C++11) remove_cvref (C++20) enable_if (C++11) void_t (C++17) conditional (C++11) common_type (C++11) common_reference (C++20) underlying_type (C++11) result_ofinvoke_result (C++11)(until C++20*)(C++17) type_identity (C++20)
Compile-time rational arithmetic
Compile-time integer sequences
integer_sequence (C++14)

 

Defined in header <type_traits>
template< class Fn, class... ArgTypes > struct is_invocable;	(1)	(since C++17)
template< class R, class Fn, class... ArgTypes > struct is_invocable_r;	(2)	(since C++17)
template< class Fn, class... ArgTypes > struct is_nothrow_invocable;	(3)	(since C++17)
template< class R, class Fn, class... ArgTypes > struct is_nothrow_invocable_r;	(4)	(since C++17)

1) Determines whether INVOKE(std::declval<Fn>(), std::declval<ArgTypes>()...) is well formed when treated as an unevaluated operand.

2) Determines whether INVOKE<R>(std::declval<Fn>(), std::declval<ArgTypes>()...) is well formed when treated as an unevaluated operand.

3) Determines whether INVOKE(std::declval<Fn>(), std::declval<ArgTypes>()...) is well formed when treated as an unevaluated operand, and is known not to throw any exceptions.

4) Determines whether INVOKE<R>(std::declval<Fn>(), std::declval<ArgTypes>()...) is well formed when treated as an unevaluated operand, and is known not to throw any exceptions.

Fn, R and all types in the parameter pack ArgTypes shall each be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.

If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.

The behavior of a program that adds specializations for any of the templates described on this page is undefined.

Helper variable templates

Defined in header <type_traits>
template< class Fn, class... ArgTypes > inline constexpr bool is_invocable_v =     std::is_invocable<Fn, ArgTypes...>::value;	(1)	(since C++17)
template< class R, class Fn, class... ArgTypes > inline constexpr bool is_invocable_r_v =     std::is_invocable_r<R, Fn, ArgTypes...>::value;	(2)	(since C++17)
template< class Fn, class... ArgTypes > inline constexpr bool is_nothrow_invocable_v =     std::is_nothrow_invocable<Fn, ArgTypes...>::value;	(3)	(since C++17)
template< class R, class Fn, class... ArgTypes > inline constexpr bool is_nothrow_invocable_r_v =     std::is_nothrow_invocable_r<R, Fn, ArgTypes...>::value;	(4)	(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if (for overload (1)) INVOKE(std::declval<Fn>(), std::declval<ArgTypes>()...) is well formed when treated as an unevaluated operand, false otherwise (public static member constant)

Member functions

operator bool	converts the object to bool, returns value (public member function)
operator() (C++14)	returns value (public member function)

Member types

Type	Definition
value_type	bool
type	std::integral_constant<bool, value>

Notes

Feature-test macro	Value	Std
__cpp_lib_is_invocable	201703L	(C++17)	std::is_invocable, std::invoke_result

Examples

Run this code

#include <type_traits>
 
auto func2(char) -> int (*)()
{
    return nullptr;
}
 
int main()
{
    static_assert(std::is_invocable_v<int()>);
    static_assert(not std::is_invocable_v<int(), int>);
    static_assert(std::is_invocable_r_v<int, int()>);
    static_assert(not std::is_invocable_r_v<int*, int()>);
    static_assert(std::is_invocable_r_v<void, void(int), int>);
    static_assert(not std::is_invocable_r_v<void, void(int), void>);
    static_assert(std::is_invocable_r_v<int(*)(), decltype(func2), char>);
    static_assert(not std::is_invocable_r_v<int(*)(), decltype(func2), void>);
}

See also

invokeinvoke_r (C++17)(C++23)	invokes any Callable object with given arguments and possibility to specify return type (since C++23) (function template)
result_ofinvoke_result (C++11)(removed in C++20)(C++17)	deduces the result type of invoking a callable object with a set of arguments (class template)
declval (C++11)	obtains a reference to its argument for use in unevaluated context (function template)
invocableregular_invocable (C++20)	specifies that a callable type can be invoked with a given set of argument types (concept)