Stewart, Robert skrev:
Scott McMurray wrote: On Thursday, March 05, 2009 10:24 PM
really don't, for example, see why the self-assignment check is worth omitting.
The conditional leads to predictive execution by modern CPUs. If the predicted outcome of the conditional differs from reality, the pipeline stalls. Thus, the canonical copy assignment operator uses copy-and-swap. That reuses the cctor logic and the (expected) efficiency of swap() to make copying safe and efficient without the need for a self-assignment check.
In those rare situations in which self-assignment actually occurs, profiling might reveal the extra copying and swapping and expose the need to redesign the calling code. For the normal use case, the non-checking copy assignment operator will be as efficient as possible.
Unfortunately, the caninical operator=(T) that swaps is not efficient for this container. -Thorsten