std::convertible_to(3)

💖 std::convertible_to(3) 💖

okay so this is the std::convertible_to(3) page from the C++ Standard Libary (that spelling is straight from the header, bestie, not me 😭). buckle up, we're talking concepts and conversions and it's gonna be iconic 🫶

✨ NAME ✨

• std::convertible_to — literally std::convertible_to, that's the name, no cap 💅

🌸 Synopsis 🌸

Defined in header <concepts> — yes bestie, that exact header 🎀

template< class From, class To >

concept convertible_to =
    std::is_convertible_v<From, To> &&          (since C++20)
    requires {
        static_cast<To>(std::declval<From>());

    };

The concept convertible_to<From, To> says 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. it's giving "both roads lead to the same slay" ✨

🦋 Semantic requirements 🦋

So 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 — these things are true:

• 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). that's the rule, bestie, no exceptions unless the page says so 💅

👀 See also 👀

• is_convertible (C++11) (class template) and is_nothrow_convertible (C++20) — checks if a type can be converted to the other type.

std::convertible_to(3) · source/version: http://cppreference.com · date: 2024.06.10 — okay bye bestie, go convert responsibly 💖✨