Errors, bugs, questions - page 1705

[fxsaber]

fxsaber:
Stupid. Can you tell me why you can't do that?

Got it.

[TheXpert]

fxsaber:
Got it.

Explain

[fxsaber]

Комбинатор:
Explain

It won't work - there's a terminology gap.

[Sergei Vladimirov]

Комбинатор:
Explain

this[0] here is rvalue.

[TheXpert]

Sergei Vladimirov:
here[0] is rvalue.

This is what is not clear.

If the assignment works in the first case, logically it should work in the second one as well. Because in the first case the same rvalue is assigned to the pointer, but the operator then works!

This is just my opinion, of course. But I want to make it out.

[Sergei Vladimirov]

Комбинатор:

That's what I don't understand.

I don't understand it either. )) Upd. Already got it.

If assignment works in the first case, it should logically work in the second one as well. That's because in the first case, the same rvalue is assigned to the pointer but the operator works after that!

This is, of course, just my opinion. But I want to make it out.

rvalue can only be assigned to a left-handed value or be a temporary constant.

This is what works in the pluses:

class A
{
public:
        int m[10];

        int& operator [] (const int i)
        {
                return((m[i]));
        }
};

int main()
{
        A oA;
        oA[2] = 5;
}

This one doesn't.

class A
{
public:
        int* m[10];

        int* operator [] (const int i)
        {
                return((m[i]));
        }
};

int main()
{
        A oA;
        oA[2] = new int;    // error C2106: =: левый операнд должен быть левосторонним значением
}

[TheXpert]

Sergei Vladimirov:

This one isn't, and I can't figure out the difference:

If you add a link to the pointer it will work. Or a double pointer.

[Sergei Vladimirov]

Комбинатор:
If you add a link to the pointer it will work. Or a double pointer.

I don't understand, what link, where?

[Sergei Vladimirov]

Ugh, man. In the second example operator[] returns address of the i-th element - of course, it cannot be changed. Stupid in the evening.

[TheXpert]

Oops, I'm slowing down, the second example isn't right at all.

That's why it is logical that

error: invalid initialization of non-const reference of type 'int*&' from an rvalue of type 'int*'