On 9/24/2010 9:58 PM, Robert Ramey wrote:
Eric Niebler wrote:
On 9/24/2010 8:22 PM, Robert Ramey wrote:
would all this boil down to the following guidlines.
a) All template libraries should use boost::concepts ?
Certainly Concept_check or something like it has a big role to play in this. But I wouldn't know how to use Concept_check to verify that an expression template matches a grammar, for instance. It's not the whole story. Though perhaps I don't know enough about the concept_check library to see how it can apply to proto expressions and grammars. Suggestions?
Also, I would prefer C++0x static_assert to the concept_check macros because the error messages can be much nicer. I think the answer is that the concept_check library badly needs a C++0x makeover.
Hmm - so the above guidline would be sufficient if the concept_check_library were subjected to a makeover?
Possibly. Likely, even. I just don't know enough to say.
Your article makes a point that libraries should check template parameters. It's my understanding that this is the intention of boost concept checks. I'm not sure where "verify that an expression template matches a grammar" fits in here.
Expressions are interesting in that they have such rich compile-time structure. Think of XML documents. Grammars are like XML Schemas; they describe which XML documents are valid. I just don't know how to match the schema/data model on the concept/type model. What is the concept satisfied by a Spirit rule? Or a Phoenix lambda expression? I've never seen a concept like that. I guess what I'm wondering is if concepts are really powerful enough to describe types like that.
b) All template libraries should try to factor implemenations so that compile errors are not propagated?
Yes. And: detailed comments should be left near any static assertions or concept checks, since that's where the unlucky few will end up.
I've been doing ths all the time. It's more than a few that end up there.
Just to sum up would the following be sufficent to implement your idea?
a) makeover of concept_check b) wider usage of concept_check c) refactoring to truncate listings of compiler errors
Obviously I'm trying to boil this down to something that can be verified in an objective way.
With the above caveat about whether concepts are powerful enough, yes. -- Eric Niebler BoostPro Computing http://www.boostpro.com