Boost logo

Boost :

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

IMPORTANT: The information contained in this email and/or its attachments is confidential. If you are not the intended recipient, please notify the sender immediately by reply and immediately delete this message and all its attachments. Any review, use, reproduction, disclosure or dissemination of this message or any attachment by an unintended recipient is strictly prohibited. Neither this message nor any attachment is intended as or should be construed as an offer, solicitation or recommendation to buy or sell any security or other financial instrument. Neither the sender, his or her employer nor any of their respective affiliates makes any warranties as to the completeness or accuracy of any of the information contained herein or that this message or any of its attachments is free of viruses.

Boost list run by bdawes at, gregod at, cpdaniel at, john at