220 29601 <945de37f-352d-008f-a29b-d354999c6c4c@wanadoo.fr> article
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From: "Vicente J. Botet Escriba" <vicente.botet@wanadoo.fr>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: Re: Add a "tuple_slice" function in <tuple>
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Le 30/11/2016 =C3=A0 22:53, Matthew Woehlke a =C3=A9crit :
> On 2016-11-30 16:04, =CE=9D=CE=B9=CE=BA=CF=8C=CE=BB=CE=B1=CE=BF=CF=82 =CE=
=91=CE=B8=CE=B1=CE=BD=CE=B1=CF=83=CE=AF=CE=BF=CF=85 wrote:
>> Just floating the idea before composing the complete text. I recently *b=
logged
>> <https://ngathanasiou.wordpress.com/2016/11/28/want-a-std-slice/>*about =
a
>> hypothetical tuple slice functionality (and related design consideration=
s)
>> and it seems useful & simple enough (conceptually and implementation wis=
e)
>> to be added in isolation to the Standard library (it may just have been
>> overlooked in previous versions, I couldn't find related proposals).
> If we had generalized slicing, would the proposed library function offer
> anything superior to `std::make_tuple([I1:I2]product_type...)`?
>
> (Generalized slicing would work both on *any* product type, as well as
> on parameter packs, so in at least that sense, it is superior to a
> library function that operates only on std::tuple.)
>
I agree that new algorithms should work on ProductTypes [P0327R1]. It is=20
not yet clear  to me how we would have the same syntax for ProductTypes=20
and parameter packs. I'm not saying that I'm against, just that we don't=20
have yet a clear proposal for this common access. While this could be=20
user friendly, it doesn't compose well in generic code.

I believe it is worth defining algorithms that do whatever we want=20
independently of the precise implementation and the possible language=20
evolution.

I'm considering defining some kind of ProductType views as we could have=20
Range views. product_type::slice<I1,I2>(pt) could return a lazy=20
product_type::slice_view<I1,I2, PT>. This should be more efficient,=20
needs to store a reference to the ProductType instead to a reference to=20
each one of the elements of the product type. Sorry, but I don't have=20
neither a draft paper nor an implementation to show yet.

What do you think of this suggested product type views?

BTW, would slicing [I1,I2]pt... return a pack or a product type? Or a view?

Vicente

--=20
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