Re: [boost] [utility] new auto_buffer class --- RFC

Subject: Re: [boost] [utility] new auto_buffer class --- RFC
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-03-06 08:33:08

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.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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