Copy elision

Copy elision is a compiler optimization technique used in C++ that removes unnecessary copying of objects. The language standard lets an implementation perform any optimization that leaves a program's observable behavior as if the standard had been followed exactly, and it additionally names a few situations in which copies may be dropped even though the visible behavior changes, for example when a temporary object is copied into an object of the same type. The best known case is return value optimization, in which the compiler builds a function's returned object directly in the caller's storage rather than creating a hidden temporary and copying it. Walter Bright implemented a technique of this kind in his Zortech C++ compiler around 1991, and the named variant is called named return value optimization. From C++17 the standard guarantees copy elision in certain cases, so that a value is constructed directly in its final destination. GCC offers the option -fno-elide-constructors to switch the behavior off so that the effect can be observed.