Re: [boost] [system][filesystem v3] Question about error_code arguments

Subject: Re: [boost] [system][filesystem v3] Question about error_code arguments
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-10-20 16:10:27

Andrey Semashev wrote:
> Stewart, Robert wrote:
> > Beman Dawes wrote:
> >
> > set, then there's no need for a null reference.  Unfortunately, that
> > has a performance downside: the function must be called and the
> > temporary must be created or a reference to a global object must be
> > created for all calls that use the default.  A null pointer default
> > must be cheaper.
>
> I think the performance cost of checking a reference or pointer for
> validity and checking some property in the error_code
> instance will be
> the same. After all, in both cases it comes down to a single
> comparison
> of two integers. Even if referencing the global default instance does
> add overhead, I bet it is negligible.

I wasn't referring to checking the reference or pointer.  Rather, I was pointing out that the reference must be bound to something when the default is accepted.  Every call using the default implies code that acquires an object or reference to one to which the formal parameter can be bound.  That is costlier than simply passing a null pointer unless some compiler magic is involved.

_____
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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