[boost] Formal Review: Boost.RangeEx -- Comments from Sean Parent from Adope

Subject: [boost] Formal Review: Boost.RangeEx -- Comments from Sean Parent from Adope
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2009-02-26 09:04:55

Hi Neil,

Here are some comments from Sean. I think they raises several aspects 
that we shuold discuss.
 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Some comments after taking a quick look (sorry, I don't have time for a 
full review) -

Some important range concepts are missing - specifically:

counted range (a range denoted by an iterator and an integer count)
sentinel range (a range denoted by an iterator and a sentinel, a NTBS is 
an example)

I believe such concepts could also clean up the char* vs. char[] for 
NTBS ambiguities as well as keep cstr library efficiency.

In ASL we've been slowing extending the algorithms for such cases, for 
example, see lower_bound_n.

<http://stlab.adobe.com/lower__bound_8hpp.html>

Also, the range based algorithms in ASL are not just about ranges, we 
also bind function arguments to avoid having to clutter binds in 
interfaces, "find_if(range, &my_type::member)"

We've also been extending the algorithms to take key/projection 
functions. For example:

---
struct my_type {
     int         member;
     double     another_member;
};
//...
my_type a[] = { { 1, 2.5 }, ... };
// sort the array by the first member:
sort(a, less(), &my_type::member);
my_type* i = lower_bound(a, 5, less(), &my_type::member);
---
In ASL, I believe we get far more bang out these extension then we do 
out of the range extensions.
I haven't looked at the Range.Ex code, but many such libraries refine 
mutating container algorithms such as sort() to call list<>::sort() - I 
object to refining algorithms where the semantics differ (in this case, 
std::sort(list.begin(), list.end()) is identity preserving where 
list<>::sort() is not. I would rather see the introduction of node based 
algorithms, such as sort_nodes() and specialize those for list<>.
The addition of bounded functions (which take output ranges) would also 
be a nice addition - see copy_bounded as an example:
<http://stlab.adobe.com/group__copy.htm>
If anyone would like to take the code from ASL as a starting point for 
inclusion in boost, they have my permission.
Sean