Re: [boost] Formal Review: Boost.RangeEx

Subject: Re: [boost] Formal Review: Boost.RangeEx
From: Neil Groves (neil_at_[hidden])
Date: 2009-02-25 12:29:08

Dear Giovanni,

On Wed, Feb 25, 2009 at 5:13 PM, Giovanni Piero Deretta <gpderetta_at_[hidden]
> wrote:

> On Wed, Feb 25, 2009 at 5:32 PM, Neil Groves <neil_at_[hidden]>
> wrote:
> > Dear Giovanni,
> >
> > On Wed, Feb 25, 2009 at 4:21 PM, Giovanni Piero Deretta <
> gpderetta_at_[hidden]
> >> wrote:
> >
> >> On Wed, Feb 25, 2009 at 5:00 PM, Neil Groves <neil_at_[hidden]>
> >> wrote:
> >> > Dear Sir,
> >> >
> >> > On Wed, Feb 25, 2009 at 3:36 PM, Rogier van Dalen <rogiervd_at_[hidden]
> >> >wrote:
> >> >
> >> >> I am not sure I understand the motivation for the operator| syntax.
> Why
> >> >> couldn't
> >> >>        vec | boost::adaptors::reversed | boost::adaptors::unique
> >> >> be written
> >> >>        boost::adaptors::unique (boost::adaptors::reversed (vec))
> >> >> ? I think this contrast would be fairer than what the documentation
> >> >> currently has. Is there a reason why it is not possible to provide
> both
> >> >> syntaxes? The pipe syntax is nice, but sort of restricts operations
> to 1
> >> >> range in, 1 range out. Relatedly:
> >> >>
> >> >
> >> > In the adaptors section the preference for operator| is documented. It
> >> > simply chains better in my opinion.
> >> >
> >> > I do provide both alternatives, for example
> >> >
> >> > boost::make_uniqued_range(rng) is equivalent to rng | uniqued
> >> >
> >>
> >> IMHO the make_... syntax for range adaptors is horrible (i don't even
> >> like the past tense, why not just unique?).
> >> But why use two different names in the first place? Why not make
> >>
> >
> > I simply dislike lots of overloading particularly where the semantics are
> > different. Perhaps the semantics aren't that different.
>
> IMHO they are  the same thing. I think of operator() in  ' a | b' as
> 'b(a)', i.e as a generic apply operator.
>

Yes, I think I might have over-emphasised the difference. Would you prefer
the function overload to be in the boost::adaptors namespace, the boost
namespace or something else?

>
> >I had considered
> > creating a range adaptor to be highly different to applying an algorithm,
> > perhaps I over-emphasised this distinction when making the decision.
>
> FWIW, I have code like this:
>
> total = ( r | filter(_r, f) | map(_r, m) | accumulate(_r, zero, a)  );
>
> i.e. I don't have a strong distinction between adaptor and algorithms.
>

Yes, I'm sold!

>
> <snip>
> >>
> >> 'some_functor(range) ' eqivalent to 'range | some_functor'
> >>
> >> (i would actually go for the syntax 'range | some_functor(_r)', where
> >> _r is a placeholder for the range; This is usefull for adaptors that
> >> actually have other parameters in addition to the range itself)
> >>
> >
> > I would always prefer the '|' syntax to any normal function invocation
> > however it is spelled. In my opinion, it combines much more elegantly.
> >
>
> I use the '|' syntax a lot when writing long pipelines because it
> avoids long nested expressions (it also reads better left to right).
> But when I need a simple map or filter before passing a range to an
> algorithm I usually just go for the function call variant.
>
> Also, if you have a range of ranges and want to map the nested ranges,
> having 'transformed' as a function object becomes very useful:
>
> range_of_ranges | transformed(transformed(f)));
>
(and BTW, what about  renaming 'transformed' -> 'map' and 'filtered'
> -> 'filter')
>

I don't think the suggestion to change transformed is a good idea.
transformed is more obviously related to transform, and map is already a
standard container.

filtered to filter doesn't sound bad, not does uniqued to unique, as long as
it doesn't clash with other names. Perhaps this suggests that they should be
kept in the boost::adaptors namespace.

>
> --
> gpd

Neil Groves

>
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