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digitalmars.D - std.algorithm.splitter defect: isTerminator version does not return

reply "monarch_dodra" <monarch_dodra gmail.com> writes:
The "isTerminator" version of std.algorithm.splitter, eg:
auto splitter(alias isTerminator, Range)(Range input)

Returns an object that is "only" ForwardRange. This is especially 
weird, since the normal "separator" version is bidirectional. 
Comparing using a function rather than with a value should have 
no difference...

This defect "leaks" into std.array.splitter, defined as:

auto splitter(C)(C[] s)
     if(isSomeString!(C[]))
{
     return std.algorithm.splitter!(std.uni.isWhite)(s);
}

Here is some code reproducing it:

----
import std.array;
import std.algorithm;
import std.stdio;

void main()
{
   string s = "  hi!  my name is Monarch  ";
   auto words = std.array.splitter(s);
   if(words.front == "") words.popFront();
   if(words.back == "") words.popBack(); //What???
   foreach(word; words)
     writeln(word);
}
----

Kind regards,
Monarch Dodra
Jun 30 2012
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 6/30/12 7:21 AM, monarch_dodra wrote:

 The "isTerminator" version of std.algorithm.splitter, eg:
 auto splitter(alias isTerminator, Range)(Range input)

 Returns an object that is "only" ForwardRange. This is especially weird,
 since the normal "separator" version is bidirectional. Comparing using a
 function rather than with a value should have no difference...


I think that may as well be an oversight in the implementation of splitter.

Andrei
Jun 30 2012
parent "monarch_dodra" <monarch_dodra gmail.com> writes:
On Saturday, 30 June 2012 at 14:01:08 UTC, Andrei Alexandrescu 
wrote:

 On 6/30/12 7:21 AM, monarch_dodra wrote:

 The "isTerminator" version of std.algorithm.splitter, eg:
 auto splitter(alias isTerminator, Range)(Range input)

 Returns an object that is "only" ForwardRange. This is 
 especially weird,
 since the normal "separator" version is bidirectional. 
 Comparing using a
 function rather than with a value should have no difference...


 I think that may as well be an oversight in the implementation 
 of splitter.

 Andrei


Hi Andrei, thanks for the answer.

I would have thought as well. however, upon inspection, it would 
appear the algorithm uses std.range.take, which does not allow 
support for bidirectional ranges. I started another thread about 
it here:
http://forum.dlang.org/thread/pzudyijsfcpwlqermwke forum.dlang.org

This looks to me like a language (range) defect. I would love to 
hear your thoughts on it.

Kind Regards,
Paul
Jun 30 2012