[boost] [Review] Fusion

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2006-05-13 21:57:03

My review of the Fusion library follows, but I'll spoil the ending  
now: I vote to accept Fusion into Boost.

I was very interested to look into this library. I've found  
heterogeneous sequences to be extremely interesting and, in some  
cases, precisely the right answer. I've had to write about 1/3 to 1/2  
of the heterogeneous algorithms provided by Fusion at various times,  
time which could have been saved and code that could have been  
cleaner if Fusion was around. So, I'm quite familiar with  
heterogeneous containers and algorithms.

I was not able to review the library in-depth, unfortunately, but I'm  
itching to get my fingers on it when time allows. So, what follows is  
really just a bunch of minor nits from reading the documentation.

Overall:
   - I'm not a fan of naming libraries anything but what they do.  
"Fusion" makes sense when you understand the context, but nobody  
searching through the list of libraries will see "Fusion" and think  
"AHA! That's what I need". Alas, I don't have a name in mind.

Description:
   - Spelling error: "hetrogenous"

Introduction:
   - Parts of the introduction are a bit too colloquial for my taste,
   in particular, the paragraph.

     "Hmmm, kinda reminds us of STL right? Right! Can you imagine how it
     would be like if you used STL without the algorithms? Everyone
     will have to reinvent their own algorithm wheels."

   I'd rather see them written in a more direct manner. Not that I
   prefer boring, but at some point the whimsical writing trivializes
   the library.

Top of the Iceberg:
   - In the [1] footnote, spelling error: "Orgainization"

Support:

   tag_of: I believe I understand the usefulness of this trait, but
   only because I understand tag dispatching already. Could the
   description be expanded a little, to at least say that tags uniquely
   identify the kind of sequence or iterator, e.g., list, map, etc.?

   category_of: I'm not keen on using the same trait (category_of) for
   two different kinds of entities (sequences and iterators). Traits
   classes should be tied to a particular concept, so I'd much rather
   see separate "iterator_category" and "sequence_category"
   metafunctions.

   pair: I tripped over the name of this entity a bit. It's a little
   odd to have a "pair" with only one kind of data. I guess I'd feel
   better if this were called "keyed_value" or "key_value", because
   it's easier for me to copy with a typed key than it us for me to
   have a pair that's very different from std::pair.

Iterators:

   distance: Is the return type of distance(i, j) "int" or "convertible
   to int"? I could imagine that in many cases it could be an
   integral_constant<int, N>...

It looks like Joel and Dan did a great job.

        Cheers,
        Doug