Re: Heterogenous lists [ was Re: [boost] BGL: property "num" members ]

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-01-15 19:45:41

I propose you use std::multimap as an object. The value_type is a
pair<key,data>. No problems with constness, like we have in runtime maps,
either!

----- Original Message -----
From: "Emily Winch" <emily_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Tuesday, January 15, 2002 5:02 PM
Subject: Heterogenous lists [ was Re: [boost] BGL: property "num" members ]

>
> -----Original Message-----
> From: David Abrahams <david.abrahams_at_[hidden]>
>
>
> >----- Original Message -----
> >From: "Jeremy Siek" <jsiek_at_[hidden]>
>
> >> Also, it would be nice if we could get the heterogenous list into boost
> >> soon. Though I would prefer the name mpl::associative_list instead.
> >
> >Agreed. Emily, are you planning to submit?
>
> Yep. Only, I went to tidy it up, and then I realised that every design
> decision I made was with the intent to mock up a quick proof-of-concept
for
> the paper, and not to actually produce decent code :-)
>
> So then I discovered a nasty issue with my plot to have clones of the
> standard algorithms that work on this kind of list. In brief: How do the
> names get out of the list and into the functors called by the algorithms?
> and crucially, How can I do that while keeping my algorithms general to
> _all_ compile time object lists (e.g. boost::tuple, or some future
> heterogenous_vector), and without making the algorithm implementations
> smell?
>
> That begs the question, do the functors need to know the names? Can anyone
> think of a use for an associative_list that would require that? The paper
> mentions some, but none of them to my mind are sufficient to justify the
> capability without more concrete evidence that they'd be useful to someone
> in real life.
>
> I'm just hoping that there aren't _other_ attributes (apart from names)
that
> items in hypothetical heterogenous container implementations might need to
> introduce to functors. Otherwise each element of a heterogenous container
> would need a heterogenous container of attributes :-)
>
> Emily.
>
>
>
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