std::convertible_to

template <class From, class To>
concept convertible_to =
  std::is_convertible_v<From, To> &&
  requires {
    static_cast<To>(std::declval<From>());
  };

The concept convertible_to<From, To> specifies that an expression of the same type and value category as those of std::declval<From>() can be implicitly and explicitly converted to the type To, and the two forms of conversion are equivalent.

Semantic requirements

convertible_to<From, To> is modeled only if, given a function fun of type std::add_rvalue_reference_t<From>() such that the expression fun() is equality-preserving,

• Either
  • To is neither an object type nor a reference-to-object type, or
  • static_cast<To>(fun()) is equal to []() -> To { return fun(); }(), and
• One of the following is true:
  • std::add_rvalue_reference_t<From> is not a reference-to-object type, or
  • std::add_rvalue_reference_t<From> is an rvalue reference to a non-const-qualified type, and the resulting state of the object referenced by fun() is valid but unspecified after either expression above; or
  • the object referred to by fun() is not modified by either expression above.

Equality preservation

Expressions declared in requires-expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).

See also