Difference between revisions of "cpp/named req/ValueSwappable"
From cppreference.com
m (Text replace - "referencable" to "referenceable") |
m (~ modernized with `= delete`) |
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| Line 22: | Line 22: | ||
class IntVector { | class IntVector { | ||
std::vector<int> v; | std::vector<int> v; | ||
| − | + | // IntVector& operator=(IntVector); // not assignable (C++98 way) | |
public: | public: | ||
| + | IntVector& operator=(IntVector) = delete; // not assignable | ||
void swap(IntVector& other) { | void swap(IntVector& other) { | ||
v.swap(other.v); | v.swap(other.v); | ||
Revision as of 10:14, 27 September 2020
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
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 }
