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Subject: Re: [boost] [system][filesystem v3] Question about error_codearguments
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-10-29 08:42:10

Domagoj Saric wrote:
> "Emil Dotchevski" <emildotchevski_at_[hidden]> wrote in message
> >On Wed, Oct 28, 2009 at 12:40 PM, Detlef Vollmann
> <dv_at_[hidden]> wrote:
> >> Domagoj Saric wrote:
> >>>
> >>> ~error() ( if ( !inspected ) throw actual_error_; )
> >
> >A library should either throw when the error is detected or
> >not. If it
> >doesn't, the user might still throw, but the *library* throwing later
> >seems a very bad idea. Not to mention the issue that throwing in a
> >destructor can end up calling abort().
> if you just ignore the return...the function will appear to
> throw just as if it
> threw 'from within'...if you inspect it it 'magically' starts
> to behave as if it does not throw but returns an error code...

>From a debugging perspective, the exception will be thrown at the wrong point.

> ..._only_ if you save the returned object into a local scoped
> variable _and_ do
> not inspect it can the issues of "library after throw" and
> "abort on exception
> in destructor during unwind" come into play...

The complexity of this magical behavior, the problem with throwing in the caller rather than at the point of error, the overhead of checking to see whether to throw at each call site, and the danger of throwing in the destructor during stack unwinding, makes overloading each affected function a pleasant alternative.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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