当前位置: 首页 > 工具软件 > coNCePTuaL > 使用案例 >

C++'s mutable and conceptual constness

潘国源
2023-12-01

c++ 中的 mutable 关键字是什么意思?

mutable is for the case where an object is logically constant, but in practice needs to change. 

 

class Employee {
public:
Employee(const std::string & name)
: _name(name), _access_count(0) { }
void set_name(const std::string & name) {
_name = name;
}
std::string get_name() const {
_access_count++;
return _name;
}
int get_access_count() const { return _access_count; }

private:
std::string _name;
mutable int _access_count;
};

 

class MathObject {
public:
MathObject() : pi_cached(false) { }
double pi() const {
if( ! pi_cached ) {
/* This is an insanely slow way to calculate pi. */
pi = 4;
for(long step = 3; step < 1000000000; step += 4) {
pi += ((-4.0/(double)step) + (4.0/((double)step+2)));
}
pi_cached = true;
}
return pi;
}
private:
mutable bool pi_cached;
mutable double pi;
};

 

More details: 

http://www.highprogrammer.com/alan/rants/mutable.html

转载于:https://www.cnblogs.com/yayagamer/archive/2012/01/12/2320833.html

 类似资料: