[boost] RangeEx review

Subject: [boost] RangeEx review
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2009-03-10 10:51:22

Here is a quick review of RangeEx.

 > - Do you think the library should be accepted as a Boost library?

Yes, assuming issues raised in the recent discussions are addressed, and 
that people agree on the naming.

 > - What is your evaluation of the design?

It is nice and pretty. Here are a few comments:

- I am unsure about the syntax of the unified return type system. It's 
very practical, however, but not so pretty.

- Fusion of the function syntax and pipe syntax for adaptors would be 
useful, so that both range | transformed(f) and transformed(range, f) 
may be written.

- Relying on standard algorithms means that the functors have to provide 
a result_type. I would like the functors to be automatically wrapped so 
that boost::result_of can be used instead. I don't know if 
Boost.Iterator needs it too.

- In the sandbox version, find(range) used to call range.find() if range 
had a find member (the has_find meta-function had a poor implementation, 
but that could have been solved). I don't know why this feature was 
removed, but I personally liked that better.

- I would like to library to also provide lazy range generators, 
potentially defining an infinite range recursively.

- Adaptors for type filtering within heterogeneous sequences (sequences 
of "potentially smart" pointers, sequences of variants, sequences of 
any...) would also be a plus.
It's basically a filter+transform at the same time.

I found such an adaptor primitive very practical when dealing with 
trees, for example.

 > - What is your evaluation of the implementation?

It seems good. It's mostly just forwarding things to standard algorithms 
or Boost.Iterator for adaptors, nothing much to say.

 > - What is your evaluation of the documentation?

Simple, but doesn't necessarily need to be more complicated.

 > - What is your evaluation of the potential usefulness of the library?

Huge. I deal with sequences (or ranges) of objects everyday, and being 
able to express operations directly on them would make my code simpler 
and clearer.

 > - Did you try to use the library? With what compiler? Did you have 
any problems?

I used an old version from the sandbox, with a few custom modifications, 
less than a year ago to code some experimental proof-of-concept C++ 
wrapper over a hierarchical thread scheduler written in C (a component 
which mapped trees of tasks to trees of processors) so as to see how it 
could make the code more high-level.
This was done with GCC 4.2. I didn't have problems except making it work 
with a lambda DSEL (I actually cheated and used typeof for return type 
deduction everywhere at the time).

 > - How much effort did you put into your evaluation? A glance? A quick 
- reading? In-depth study?

I only quickly read the documentation and gave a glance at the version 
under review; but I did study the sandbox version more in-depth.

 > - Are you knowledgeable about the problem domain?

I know about ranges, iterators, functional programming, and lazy 
sequences fairly well.