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Subject: Re: [boost] [contract] toward N3351 concepts
From: Andrew Sutton (asutton.list_at_[hidden])
Date: 2012-10-06 09:11:39

> Does compiler have the authority (from formal point of view of C++
> axioms) to stop compilation with error in such case(of course, if it
> able to diagnose that)?

I believe it should, but I do not know the mechanism that it should
use to diagnose the error.

> If compiler has right to reject wrong axioms when he able to diagnose,
> then we can't use C++ axioms to express in code our assumption about
> floating-point addition associativity.

Whatever mechanism is eventually designed to check axioms would have
to accommodate floating point issues. This is an area of active
investigation. What you had in n3351 and 2887 were initial attempts to
say, in general, what was desired, but not exactly how it should work.

In n3351, we didn't know what we wanted the compiler to do with
axioms; describing language mechanics wasn't the primary focus of that
work. In n2887, the authors had a better idea of what they wanted, but
didn't (if I'm recalling correctly) specify the mechanics of how they
could be checked.

> So, I am confused about real intention.

The intent is to state requirements. Translating that to a working
language specification is a work in progress.


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