Question

I have a function

void h(A const a){...};

Is it possible that the behaviour will change if I make it:

void h(A const &a){..same body as above..};

You are free to define the type A as you wish. Of course.

Answer 1

In the first overload, h cannot change ‘a’. It is for all purposes const in the body of ‘h’.
However, this involves a copy constructor to copy initialize ‘a’.

Therefore, in the first case, it requires an accessible copy constructor in ‘A’. By the same token, it requires an accessible destructor in A.

In the second case, there is no copy initialization required, hence no accessible copy constructor/destructor of ‘A’s is required.

Also, in the first case ‘a’ will undergo ‘slicing’ if a derived object of ‘A’ is passed as argument. The second function will not have the ‘slicing’ issue as base class references can bind to derived objects. Hence, an accessible destructor is also not needed in this case.

In C++11, the first function would require ‘A’ to have an accessible ‘copy’ or ‘move’ constructor depending on how ‘h’ is invoked.