Re: [boost] Formal Review: Concept Checking Library

From: Jeremy Siek (jsiek_at_[hidden])
Date: 2000-11-25 11:52:32

On Fri, 24 Nov 2000, Beman Dawes wrote:
>  >class class_requires_test
>  >{
>  >  typedef class_requires< EqualityComparableConcept<int> >::check req1;
> 
> That's not so good.  The "typedef", "::check", and "req1" detract from the 
> clarity of the code.  I worry developers will shy away from using concept 
> checks because of the ugly code.
> 
> Another worry: in testing an early compile time asserts proposal which used 
> a similar typedef technique, I found a number of slight coding mistakes 
> would compile OK, but not actually do the indicated check.  What happens if 
> a user codes any of these mistakes (where X is a UDT that isn't Equality 
> Comparable)?

I performed these tests using g++:

>      class_requires< EqualityComparableConcept<X> >::check req1;
This compiles, but I can rig things to make it fail.

>      class_requires< EqualityComparableConcept<X> >::check;
This compiles :( Wierd, I didn't think this would compile.

>      class_requires< EqualityComparableConcept<X> > req2;
This compiles, but I can rig it to fail.

>      class_requires< EqualityComparableConcept<X> >;
This compiles :(

>      typedef class_requires< EqualityComparableConcept<X> > req3;
>      typedef class_requires< EqualityComparableConcept<X> >;
Both of these also compile :(

> If they fail to compiler, fine, but if they compile without error, and fail 
> to detect the error, I would be concerned.  If they did error check OK, but 
> generated code because the typedef was missing, that would also be a 
> concern. Could you give them a try?
> 
> While the macros were, well, macros, they were also very clear, and seemed 
> hard to misuse IMO.

There is also some hidden nastyness in the macros. For example, the type
arguments to the macros cannot contain commas or spaces, or other
non-identifier characters.

However, on the whole, I think you are right. I'll keep the
BOOST_CLASS_REQUIRES macros.

Cheers,

Jeremy

----------------------------------------------------------------------
 Jeremy Siek                        www: http://www.lsc.nd.edu/~jsiek/
 Ph.D. Candidate                  email: jsiek_at_[hidden]
 Univ. of Notre Dame         work phone: [phone]
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