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digitalmars.D - D2 Feature?

reply Patrick Kreft <patrick_kreft gmx.net> writes:
I want to know  that concept like C++0x is planing for D?
Would improve policy-based class design ^^
Regards
Patrick Kreft
Oct 09 2007
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
Patrick Kreft wrote:

 I want to know  that concept like C++0x is planing for D?
 Would improve policy-based class design ^^
 Regards
 Patrick Kreft


I don't think so, but if I remember correctly, someone already
implemented C++0x style concepts as a library (sorry; can't seem to find
the post at the moment).

	-- Daniel
Oct 09 2007
next sibling parent reply jcc7 <technocrat7 gmail.com> writes:
== Quote from Daniel Keep (daniel.keep.lists gmail.com)'s article

 Patrick Kreft wrote:

 I want to know  that concept like C++0x is planing for D?
 Would improve policy-based class design ^^
 Regards
 Patrick Kreft


 I don't think so, but if I remember correctly, someone already
 implemented C++0x style concepts as a library (sorry; can't seem to find
 the post at the moment).
 	-- Daniel


Are you guys talking about "futurism"?
http://www.dsource.org/projects/futurism

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.announce&article_id=6762
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.announce&article_id=6827
Oct 10 2007
parent Patrick Kreft <patrick_kreft gmx.net> writes:
jcc7 schrieb:

 == Quote from Daniel Keep (daniel.keep.lists gmail.com)'s article

 Patrick Kreft wrote:

 I want to know  that concept like C++0x is planing for D?
 Would improve policy-based class design ^^
 Regards
 Patrick Kreft


 I don't think so, but if I remember correctly, someone already
 implemented C++0x style concepts as a library (sorry; can't seem to find
 the post at the moment).
 	-- Daniel


 
 Are you guys talking about "futurism"?
 http://www.dsource.org/projects/futurism
 
 http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.announce&article_id=6762
 http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.announce&article_id=6827
 
 
 


No that isnt that what i want ;o It's more like i can write down, which 
Interfaces have to implemented by an class template. If i didnt 
implemented it, the compiler will give me a warning.
Oct 10 2007
prev sibling parent Reiner Pope <some address.com> writes:
Daniel Keep wrote:

 Patrick Kreft wrote:

 I want to know  that concept like C++0x is planing for D?
 Would improve policy-based class design ^^
 Regards
 Patrick Kreft


 
 I don't think so, but if I remember correctly, someone already
 implemented C++0x style concepts as a library (sorry; can't seem to find
 the post at the moment).
 
 	-- Daniel


I don't know if this is what you mean, but a while ago when concepts
were discussed, I posted a proof-of-concept ( :-) )implementation:
http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=51849

I haven't looked at it recently, but from memory, it allows both sides
of concept checking (checking that your template only uses the features
specified in the concept, and checking that the template parameters
match the required concept), albeit somewhat verbosely, by effectively
writing a one-line "static unittest" which instantiates your template
with the minimum requirements, and also single static assert in the
template requiring that the parameter matches the concept.

At the time, I didn't think overloading was possible, because the
compile would simply fail if the static assert failed. However, Sean
Kelly (I think) recently posted a clever way to get around this:

void foo(T, bool TMatches : bool = MatchesConcept!(T))(T t) {...}

This is a good step further, as it allows overloads, but it doesn't
handle the case where two overloads match, yet one should be more
specialised than the other. For instance, if one template works on the
Iterator concept and one works on the RandomAccessIterator concept, it
should choose the RandomAccessIterator, but currently it just gives an
ambiguity error.



Overall, though, I think a library implementation would be very verbose
in comparison to C++ (or Haskell type-classes), the fundamental reason
being the need to write a "static unittest" for every template and a
Sean Kelly-inspired bool specialisation for every concept-checked
template parameter. When you consider that this checking should ideally 
be written for every templated function you write, it becomes excessive.

To make it nice, some form of compiler assistance is required.

    -- Reiner
Oct 11 2007