Wednesday, April 1, 2009

pbref/pbclone -- indistinguishable by func call (restriction on overloading

At end of a function, You often see "return someNonRefVar" or "return *ptr", or "return someRef". Such a return can either return by ref or return by clone, but which one exactly? Answer is in the func prototype. Return by ref is always indicated there, not in return statements.

Quiz: by looking at the return statement itself, can you tell if it's return by clone or return by ref?
A: if it returns a non-var like "return amount + 3.22" ==} can't be pbref.
A: if it returns a local object ==} can't be pbref as the local object would self-destroy right away. But see post on RVO

It's instructive to compare with argument passing syntax. Calling code doesn't need to know to call by clone or call by ref. The func call looks identical [1] -- just put vars in the parentheses. To tell a call-by-ref func from a call-by-clone func, Key is the func prototype.

Q: Can 2 otherwise identical functions overload each other simply based on the "&" in a param?
A: no. Compiler can't "bind" a function call. I tested in gcc. Also covered in IKM test.

[1] except you can't pass non-vars in pbref.

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