On Wed, Sep 26, 2012 at 12:00 PM, Lorenzo Caminiti <lorcaminiti@gmail.com> wrote:
However, N3351 says that axioms should not be checked by the compiler...
``Axioms express the semantics of a concept’s required syntax; they are assumed to be true and must not be checked by the compiler beyond conformance to the C++ syntax. Any additional checking is beyond the scope of the compiler’s translation requirements. The compiler must not generate code that evaluates axioms as preconditions, either. This could lead to program errors if the evaluated assertions have side effects. For example, asserting that distance(first, last) > 1 when the type of those iterators is istream_iterator will consume the first element of the range, causing the assertion to pass, but the algorithm to have undefined behavior.''
So what am I supposed to do with axioms? Do nothing? Axioms are just "comments" that document the semantic?
All: I'm still struggling with my original question... what am I supposed to programatically do with axioms? Take a look at this axioms--is_valid is not implementable... what would I check here? concept BidirectionalIterator<ForwardIterator I> = ... requires decrement (I i, I j) { ... axiom { is_valid(––i) <=> is_valid(i––); is_valid(i––) => (i == j => i–– == j); is_valid(i––) => (i == j => (i––, i) == ––j); } Same thing for the magic eq() that is not implementable (if not trivially as operator==). And if we get rid of eq and define <=> as equivalence instead of iff then <=> is not implementable. Even just checking axiom's syntax... what does that mean if I cannot implement eq, is_valid, <=>, etc? I don't understand... It seems to me that we are writing axioms using a bunch of non-implementable operations... IMO, if axioms cannot be checked programatically, either syntactically at compile-time and/or with run-time assertions, then they should just be noted as code comments... Why would I program (axiom) code that is neither compiled nor executed? Thanks, --Lorenzo