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Subject: Re: [boost] [system] Would it be possible to trial a breaking change to Boost.System and see what happens?
From: Peter Dimov (lists_at_[hidden])
Date: 2018-01-15 14:53:40

Christopher Kohlhoff wrote:
> >> Why must this exist? (With the emphasis placed on "generic".)
> >
> > For the reason I stated; so that one can write a function whose logic is
> > not broken when a callee switches (or is switched, or is ported) to
> > another implementation and starts returning error codes from a different
> > domain.
> This is not logical. Part of being able to switch backends is that both
> backends adhere to a given specification. In the error handling model in
> your example, this specification would stipulate that on failure a
> function produces a non-zero-valued error code. Producing the errors from
> a different domain doesn't change that fact. However, this property is
> independent of the error_code itself; it is a property of your
> specification.

This is circular reasoning. My specification would return success when the
function succeeds. How would it return success is determined by what is the
established way to return success. The current de-facto standard way of
returning success is zero, so I'd specify my function to return that. Were
the standard way to signal success something else, my specification would
reflect that something else.

> Originally you phrased it as a generic way to test for failure, but I
> think I mostly agree with you if you instead phrase it in terms of success
> (as you are now doing).

These two ways to phrase it are the same; generic success and generic
failure to succeed are complementary. Today, the logic is expressed in terms
of if(ec) and if(!ec); whether the function tests for failure

    do_f1( ec );
    if( ec ) return;

    do_f2( ec );

or for success

    do_f1( ec );
    if( !ec ) do_f2( ec );

makes no difference.

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