std::is_callable, std::is_nothrow_callable

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

Type support

Basic types
Fixed width integer types (C++11)
Fixed width floating-point types (C++23)
ptrdiff_t size_t max_align_t (C++11)     byte (C++17)	nullptr_t (C++11) offsetof NULL
Numeric limits
numeric_limits
C numeric limits interface
Runtime type information
type_info type_index (C++11)	bad_typeid bad_cast

 

Defined in header <type_traits>
template <class, class R = void> struct is_callable; // not defined template <class Fn, class... ArgTypes, class R> struct is_callable<Fn(ArgTypes...), R>;	(1)	(since C++17)
template <class, class R = void> struct is_nothrow_callable; // not defined template <class Fn, class... ArgTypes, class R> struct is_nothrow_callable<Fn(ArgTypes...), R>;	(2)	(since C++17)

1) Determines whether Fn is callable with the arguments ArgTypes... and the result would be convertible to R. Formally, determines whether INVOKE(declval<Fn>(), declval<ArgTypes>()..., R) is well formed when treated as an unevaluated operand, where INVOKE is the operation defined in Template:concept.

2) Determines whether Fn is callable with the arguments ArgTypes... and the result would be convertible to R (same as (1)), and that such call is known not to throw any exceptions.

If Fn, R or any type in the parameter pack Args is not a complete type, (possibly cv-qualified) void, or an array of unknown bound, 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.

Helper variable templates

Defined in header <type_traits>
template <class T, class R = void> constexpr bool is_callable_v  = std::is_callable<T, R>::value;	(1)	(since C++17)
template <class T, class R = void> constexpr bool is_nothrow_callable_v = std::is_nothrow_callable<T, R>::value;	(2)	(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if INVOKE(declval<Fn>(), declval<ArgTypes>()..., R) 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

Version (1) of this trait may be implemented in terms of std::is_convertible and std::result_of.

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 an object of the template type argument for use in an unevaluated context (function template)