Re: [boost] "Simple C++11 metaprogramming"

Subject: Re: [boost] "Simple C++11 metaprogramming"
From: Peter Dimov (lists_at_[hidden])
Date: 2015-06-01 19:55:24

Bruno Dutra wrote:
> The need for so called metafunction-classes arises most naturally as soon 
> as one decides to write a metafunction that returns another metafunction. 
> As pointed out by Vincente Escriba, template aliases can't allow for an 
> indistinguishable handling of metafunctions and variables (that is types), 
> for the obvious reason they can't match template type parameters.

I actually know all that. That's kind of the point.

You can't just say "we need higher-order metaprogramming to return 
metafunctions from metafunctions" - this is a tautology. This is what 
"higher-order metaprogramming" means. You're basically saying that we need 
higher-order metaprogramming to do higher-order metaprogramming. True but 
trivial.

There obviously do exist occasions that call for higher-order 
metaprogramming. The question is can we get by in 97% of the cases without 
it. Not whether it's useful, but whether it's indispensable. Whether there's 
a room for a "simple" metaprogramming library that doesn't provide 
higher-order constructs and is therefore based on template aliases and not 
on metafunction classes, and whether such a library can be adequately useful 
for real world tasks. (I'm open to the possibility that the answer is "no", 
but I'd like it to be "yes".)