Re: [Boost-users] [mpl] newbie question

25 Feb 2006


      "David Abrahams" wrote
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"Andy Little"writes:
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"David Abrahams" wrote
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"Andy Little"  writes
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"David Abrahams" wrote
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"Andy Little" writes
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I am not concerned with the intractible problem of sequence identity
( whatever that means) at the moment.
Then what was this indictment about?
Me:
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The result of the transform is only required to be "concept-identical"
to the result you're looking for.
You:
 IMO that behaviour is sloppy.
What can I say? I acknowledge that mpl is a monumental piece of work .
Wonderful... but far from perfect.
I don't think the fact that it's imperfect gives you the right to
label any arbitrary design decision as sloppy.
I dont follow?  "any arbitrary decision"?
Yes, in this case the particular design decision that
transform  >::type
may not always be a specialization of some_template.
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You seem to have no justification at all for calling the behavior
mentioned above "sloppy," notwithstanding that it reminds you of
another behavior that you dislike.
The behaviour of having a return type defined as a concept rather
than a type in this case is unnecessarily imprecise.
You haven't proven that about transform, which is the case in
question.
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In practise (Based on my experience in pqs physical quantities
library) it causes an explosion of arbitrary types all meaning the
same thing. This in turn leads to slow compile times and overuse of
compiler resources and with the fatal effect in some cases, that the
compiler cannot cope resulting in a failed compilation.
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An alternative suggestion is to explicitly specify what seems to be
the actual behaviour of arithmetic operations on int_'s, long's etc
in the documentation.
Stop.  The statement in question is about transform, not about int_'s,
long_'s, etc.  You condemned Aleksey's design decision about the
result of transform and have repeatedly claimed that it is unnecessary
and could easily be done better.  Please demonstrate, or retract your
claim.
I think we need a little bit more context here.
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OP
David Abrahams
Andy Little (me)
Just trying to use mpl::transform on a vector of int's and I can't seem to
get
it working properly. Can anyone see what's wrong?? I'm trying to perform
vector_c + vector_c = vector_c
The is_same function always returns false when I compile and run it.
The result of the transform is only required to be "concept-identical"
to the result you're looking for.
IMO that behaviour is sloppy. I see no reason why (at least)
boost::is_same < plus< int_<1> ,int_<1> >::type, int_<2> > shouldnt
be true.
Your  change from "the transform" to "being about transform" above is
problematic for me.

regards
Andy Little