18 Concepts library [concepts]

18.4 Language-related concepts [concepts.lang]

18.4.14 Concept copy_constructible [concept.copyconstructible]

template<class T>
  concept copy_constructible =
    move_constructible<T> &&
    constructible_from<T, T&> && convertible_to<T&, T> &&
    constructible_from<T, const T&> && convertible_to<const T&, T> &&
    constructible_from<T, const T> && convertible_to<const T, T>;

If T is an object type, then let v be an lvalue of type (possibly const) T or an rvalue of type const T.

T models copy_constructible only if

(1.1)
After the definition T u = v;, u is equal to v ([concepts.equality]) and v is not modified.
(1.2)
T(v) is equal to v and does not modify v.