C++ Storage class specifiers mutable
Example
A specifier that can be applied to the declaration of a non-static, non-reference data member of a class. A mutable member of a class is not const even when the object is const.
class C {
int x;
mutable int times_accessed;
public:
C(): x(0), times_accessed(0) {
}
int get_x() const {
++times_accessed; // ok: const member function can modify mutable data member
return x;
}
void set_x(int x) {
++times_accessed;
this->x = x;
}
};
C++11
A second meaning for mutable was added in C++11. When it follows the parameter list of a lambda, it suppresses the implicit const on the lambda's function call operator. Therefore, a mutable lambda can modify the values of entities captured by copy. See mutable lambdas for more details.
std::vector<int> my_iota(int start, int count) {
std::vector<int> result(count);
std::generate(result.begin(), result.end(),
[start]() mutable { return start++; });
return result;
}
Note that mutable is not a storage class specifier when used this way to form a mutable lambda.
