Change object's field in type cast C++

Problem: when write type cast operator for object, i want to change state of object’s field, who calls cast-operation.

Question: how can i change state of field in object, which one call cast operator?

Example below:

#include <iostream>

class myClass {
public:
    int field;
    int res;
    myClass() { field = 0; res = -1; }
    operator bool() {
        field = 0;
        return static_cast<bool>(res);
    }
    myClass operator>(int val) {
        if (field > val) {
            res = 1;
        }
        else {
            res = 0;
        }
        return *this;
    }
};

int main() {
    myClass example;
    example.field = 10;
    bool conRes = static_cast<bool>(example > 5);
    return 0;
}

But field doesn’t change, cause in cast operator will sending copy of object:

test add before cast: 0000000A7BAFF6C8
test add bool() cast: 0000000A7BAFF7C4
test add after cast: 0000000A7BAFF6C8

>Solution :

I believe the problem is in the return type you have chosen for operator >. You are returning a new instance of myClass. If you would like the result to act as the original class, you should return a reference to it instead. This is done by changing the return type to include &.

myClass operator>(int val)
return *this; // return a copy of this object

myClass& operator>(int val)
return *this; // return a reference to this object

In your code, with this change the reference myClass& returned will give direct access to example and you should see that field will be set to 0 during the cast operator call.

If you are familiar with objects in other programming languages C++ may be different in this way. myClass is a new object, but there are two ways to gain access to the object from another name alias.

• myClass& is a reference, which simply becomes another name for a myClass that existed before it.
• myClass* is a pointer, which may also access an existing myClass. However, unlike a reference, the pointer can be reassigned, and changed to point at a different myClass.

So, references are used when you need an alias to access one specific object. Pointers are used when you want to access different objects over time. A pointer that is never reassigned is similar in capability to a reference.