# C++ named requirements: ValueSwappable (since C++11)

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< cpp‎ | named req

Two objects of this type can be dereferenced and the resulting values can be swapped using unqualified function call swap() in the context where both std::swap and the user-defined swap()s are visible.

### Requirements

A type T is ValueSwappable if

1. `T` satisfies the LegacyIterator requirements.
2. For any dereferenceable object `x` of type `T` (that is, any value other than the end iterator), `*x` satisfies the Swappable requirements.

Many standard library functions expect their arguments to satisfy ValueSwappable, which means that any time the standard library performs a swap, it uses the equivalent of using std::swap; swap(*iter1, *iter2);.

### Example

Run this code

    #include <iostream>
    #include <vector>

    class IntVector
    {
        std::vector<int> v;
    //  IntVector& operator=(IntVector); // not assignable (C++98 way)
    public:
        IntVector& operator=(IntVector) = delete; // not assignable
        void swap(IntVector& other)
        {
            v.swap(other.v);
        }
    };

    void swap(IntVector& v1, IntVector& v2)
    {
        v1.swap(v2);
    }

    int main()
    {
        IntVector v1, v2;    // IntVector is Swappable, but not MoveAssignable
        IntVector* p1 = &v1;
        IntVector* p2 = &v2; // IntVector* is ValueSwappable
        std::iter_swap(p1, p2); // OK: iter_swap requires ValueSwappable
    //  std::swap(v1, v2); // compiler error! std::swap requires MoveAssignable
    }

### See also

indirectly_swappable (C++20) | specifies that the values referenced by two `indirectly_readable` types can be swapped (concept)

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