std::type_order

 

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Defined in header <compare>
template< class T, class U > struct type_order;		(since C++26)

See More

Implements an implementation-defined total ordering of all types.

Provides the member constant value equal to std::strong_ordering::less if T precedes U in this implementation-defined total order, std::strong_ordering::greater if U precedes T, and std::strong_ordering::equal if they are the same type.

This ordering need not be consistent with the one induced by std::type_info::before.

The template arguments T and U can be incomplete types.

If the program adds specializations for std::type_order or std::type_order_v, the program is ill-formed.

Helper variable template

template< class T, class U > constexpr std::strong_ordering type_order_v = type_order<T, U>::value;		(since C++26)

Member constants

value [static]

a value of type std::strong_ordering, as described above (public static member constant)

Member functions

operator std::strong_ordering	converts the object to std::strong_ordering, returns value (public member function)
operator()	returns value (public member function)

Member types

Type	Definition
value_type	std::strong_ordering

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_type_order	202506L	(C++26)	std::type_order, std::type_order_v

Example

Run this code

#include <compare>
#include <meta>
#include <print>
#include <type_traits>

template <typename T, typename U>
void print_type_order()
{
    auto t{std::meta::display_string_of(^^T)};
    auto u{std::meta::display_string_of(^^U)};
    if constexpr (constexpr auto order{ std::type_order_v<T, U> }; order == 0)
        std::println("“{}” and “{}” have the same order", t, u);
    else
        std::println("“{}” goes before “{}”", order < 0 ? t : u, order < 0 ? u : t);
}

int main()
{
    template for (constexpr auto t : {^^int, ^^char, ^^int&, ^^const int, ^^long})
        print_type_order<int, typename[:t:]>();
}

Possible output:

“int” and “int” have the same order
“char” goes before “int”
“int&” goes before “int”
“const int” goes before “int”
“int” goes before “long int”

See also

strong_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is substitutable (class)
type_order (C++26)	performs a three-way comparison on reflected types (function)