std::convertible_to - cppreference.com (original) (raw)

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 produce equal results.

[edit] 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.

[edit] Equality preservation

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

[edit] References

• C++23 standard (ISO/IEC 14882:2024):

• 18.4.4 Concept convertible_to [concept.convertible]

• C++20 standard (ISO/IEC 14882:2020):

• 18.4.4 Concept convertible_to [concept.convertible]

[edit] See also