David Abrahams wrote:
In the case of copy-elision for by-value arguments and return values, the compiler is explicitly allowed to _assume_ there is no semantic difference between the original rvalue and its copy. That's low-hanging fruit for a compiler writer, that pays huge dividends.
So far I've found 7 copy assignment operators that could be improved by having their argument "by value", instead of "by const reference", at the following locations, in trunk/boost: - any.hpp(64): boost::any - function\function_template.hpp(916): boost::function - intrusive_ptr.hpp(114): intrusive_ptr - multi_index_container.hpp(269): multi_index_container - interprocess\allocators\adaptive_pool.hpp(136): adaptive_pool_base - spirit\home\classic\tree\common.hpp(101): spirit::tree_node - spirit\home\classic\tree\common.hpp(624): spirit::tree_match Am I correct, or am I possibly missing some others? I wouldn't mind creating some tickets (one per source file), requesting to have their argument "by value", as we discussed at comp.lang.c++.moderated, "Re: Is self assignment test valid?". Basically it was concluded that /if/ an assignment operator is implemented by means of copy-and-swap, it should preferably be done as follows: T& operator=(T arg) { arg.swap(*this); return *this; } And preferably /not/ as follows: T& operator=(const T & arg) { T(arg).swap(*this); return *this; } Kind regards, -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center