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Showing content from https://en.cppreference.com/w/cpp/language/../memory/../thread/../named_req/MoveConstructible.html below:

C++ named requirements: MoveConstructible (since C++11)

Specifies that an instance of the type can be constructed from an rvalue argument.

The type T satisfies MoveConstructible if

Given

• rv, an rvalue expression of type T,
• u, an arbitrary identifier.

The following expressions must be valid and have their specified effects.

The new value of rv is unspecified.

The new value of rv is unspecified.

A class does not have to implement a move constructor to satisfy this type requirement: a copy constructor that takes a const T& argument can bind rvalue expressions.

If a MoveConstructible class implements a move constructor, it may also implement move semantics to take advantage of the fact that the value of rv after construction is unspecified.

Being a MoveConstructible class implies std::is_move_constructible but not vice versa since std::is_move_constructible will only check for the ability to call the constructor with the correct arguments, not a post-condition value.

Run this code

#include <iostream>
 
struct S
{
    int n;
    S(int in) : n{in} {}
    S(S&& other) { n = other.n + 1; }
};
static_assert(std::is_move_constructible_v<S>);
 
int main()
{
    S v{1};
    std::cout << "v.n = " << v.n << '\n';
    S u = std::move(v);
 
    // Class `S` doesn't satisfy a MoveConstructible requirement
    // The value of `u` is NOT equivalent to the value of `v` before the `u` initialization
    std::cout << "u.n = " << u.n << '\n';
}

Output:

v.n = 1
u.n = 2

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

• 16.4.4.2 Template argument requirements [utility.arg.requirements]

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