Re: [boost] [MPL][vector] Is there interest in mpl::vector using variadic templates?

Subject: Re: [boost] [MPL][vector] Is there interest in mpl::vector using variadic templates?
From: Bruno Dutra (brunocodutra_at_[hidden])
Date: 2017-03-03 17:21:47

On Mar 3, 2017 17:58, "Peter Dimov via Boost" <boost_at_[hidden]> wrote:

Bruno Dutra wrote:

OTOH the void* trick requires that a pack of M void pointers be
> instantiated when the element at position M is retrieved from a list, so,
> for a list of N elements, the compiler must instantiate N *distinct* packs
> of void pointers, because each of these packs have a different size and is
> thus a distinct type.
>

Not just that, but the helper function that is required to obtain the Mth
element is a template instantiation as well.

Saying that we shouldn't use map_from_list because it consumes memory for
the instantiation is misleading; the alternatives consume memory for
instantiations as well. Except for __type_pack_element, of course.

Right, the trick is usually to figure out what consumes less memory, i.e.
what leads to the least amount of distinct template instantiations. Alias
templates help a lot with that, since they are not actually instantiated,
but there is only so much one can do with alias templates alone.

Bruno