std::tuple_size<std::complex> - cppreference.com

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template< class T > struct tuple_size<std::complex<T>> : std::integral_constant<std::size_t, 2> {};		(since C++26)

The partial specialization of std::tuple_size for std::complex provides a compile-time way to obtain the number of components of a complex, which is always 2, using tuple-like syntax. It is provided for structured binding support.

Inherited from std::integral_constant

Member constants

the constant value 2
(public static member constant)

Member functions

	converts the object to `std::size_t`, returns `value` (public member function)
	returns `value` (public member function)

Member types

Type	Definition
`value_type`	`std::size_t`
`type`	`std::integral_constant<std::size_t, value>`

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_tuple_like`	`202311L`	(C++26)	Add tuple protocol to std::complex

Example

#include <complex>

static_assert(std::tuple_size_v<std::complex<float>> == 2);

static_assert([]
{
    using namespace std::literals;
    auto [re, im] = -1.5 + 2.5i;
    return re == -1.5 && im == 2.5;
}());

static_assert([]
{
    using namespace std::literals;
    auto z = std::complex<double>{};
    auto& [re, im] = z;
    re = 1.0;
    im = 2.0;
    return z == 1.0 + 2.0i;
}());
 
int main() {}