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Subject: Re: [boost] [preprocessor] Warning: Incoming
From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2011-07-01 18:44:42

On Fri, 01 Jul 2011 08:34:35 -0700, Eric Niebler wrote:

> On 6/30/2011 11:09 PM, Paul Mensonides wrote:

>> ...but this is terrible. It doesn't take away from the point of the
>> talk, but it should be something like count<typelist<A, B, C>>, not
>> count<A, B, C>.
> I'm not disagreeing, but I'd like to know why you believe this is true
> for templates as well as macros.

I'd go further and say that it would be terrible to use variadic argument
lists (the function parameter kind, not the template parameter kind) to
as runtime data structures also. Off the top of my head, here are some

1) It forces a particular argument order. By itself, this isn't the end
of the world, but either tends to break symmetries or tends to require
argument orders to change on a bunch of other things.
2) It does not play well with overloading (via number of arguments with
macros--which you can do, via specialization of templates, or via plain
overloading of functions).
3) It frequently destroys the ability to use default arguments (which
could be accounted for if it weren't for #2).
4) It does not work when multiple data structures need to be passed (e.g.
Cartesian products).
5) It removes the ability to use the *single* variadic clump for other

I don't have a problem with variadic data used to initialize regular data
structures in the right contexts. For example, make_tuple(a, b, c). (I
do believe, however, that std::initializer_list<T> is a misfeature. I
personally think the { a, b, c } should have been mapped onto a
constructor call taking a, b, and c--which may or may not use variadic

Paul Mensonides

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