NAME¶

std::is_compound - std::is_compound

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++11)
struct is_compound;

std::is_compound is a UnaryTypeTrait.

If T is a compound type (that is, array, function, object pointer, function pointer,
member object pointer, member function pointer, reference, class, union, or
enumeration, including any cv-qualified variants), provides the member constant
value equal true. For any other type, value is false.

If the program adds specializations for std::is_compound or std::is_compound_v, the
behavior is undefined.

Template parameters¶

T - a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_compound_v = is_compound<T>::value;

Inherited from std::integral_constant

Member constants¶

value true if T is a compound type, false otherwise
[static] (public static member constant)

Member functions¶

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

Member types¶

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

Notes¶

Compound types are the types that are constructed from fundamental types. Any C++
type is either fundamental or compound.

Possible implementation¶

template<class T>
struct is_compound : std::integral_constant<bool, !std::is_fundamental<T>::value> {};

Example¶

// Run this code

#include <type_traits>
#include <iostream>

static_assert(not std::is_compound_v<int>);
static_assert(std::is_compound_v<int*>);
static_assert(std::is_compound_v<int&>);

void f();
static_assert(std::is_compound_v<decltype(f)>);
static_assert(std::is_compound_v<decltype(&f)>);

static_assert(std::is_compound_v<char[100]>);

class C {};
static_assert(std::is_compound_v<C>);

union U {};
static_assert(std::is_compound_v<U>);

enum struct E { e };
static_assert(std::is_compound_v<E>);
static_assert(std::is_compound_v<decltype(E::e)>);

struct S
{
int i : 8;
int j;
void foo();
};
static_assert(not std::is_compound_v<decltype(S::i)>);
static_assert(not std::is_compound_v<decltype(S::j)>);
static_assert(std::is_compound_v<decltype(&S::j)>);
static_assert(std::is_compound_v<decltype(&S::foo)>);

int main()
{
std::cout << "All checks have passed\n";
}

See also¶

is_fundamental checks if a type is a fundamental type
(C++11) (class template)
is_scalar checks if a type is a scalar type
(C++11) (class template)
is_object checks if a type is an object type
(C++11) (class template)
is_array checks if a type is an array type
(C++11) (class template)