On Wednesday, 7 November 2012 at 01:15:27 UTC, martin wrote:
I simply and utterly fail to comprehend the need for a compiler to distinguish between a const reference to a named variable and a const reference to an unnamed temporary/literal (which the compiler is free to allocate wherever it makes most sense).
Let me be more precise: I don't see why a called function would need to know whether a passed const reference is named or unnamed at the caller's site. The developer's reasoning for a const reference is simply to avoid costly copying of the argument to be passed (only applicable for lvalues) which is guaranteed not to be modified by the callee. Decorating such a parameter with 'const ref' seems as logical as it gets (don't pass me a copy of the real thing, pass me a reference instead - I'm not going to modify it). The only reason I can think of to distinguish between lvalues and rvalues at the callee is the slight performance hit due to pointer indirection for rvalues. And that would be addressable by preferring by-value-passing of rvalues when selecting between function overloads.
