C++ Pass By Const Reference and Return By Const Reference

Question

I\'m trying to understand if there is any benefit to returning a const reference. I have a factorial function that normally looks like this:

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Answer 1

A const reference isn't faster than a value, if the size of the value is small. In this case the type of the value is long, which is IMO small (e.g. 4 to 8 bytes): so a const reference will be no faster. In fact it may be slower, because to get the value of a reference the compiler may need to emit the code that will dereference the reference (like dereferencing a pointer).

Given that a reference is implemented (internally) like a pointer, I'd expect to get better performance from passing references than from passing values when the size of the value is bigger than the size of a pointer (assuming that it's even legal to pass a reference: a reference to a local variable that's gone out of scope isn't legal).