http://d.puremagic.com/issues/show_bug.cgi?id=4464

           Summary: std.range.take does not always return Take!R
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: yebblies@gmail.com


--- Comment #0 from yebblies <yebblies@gmail.com> 2010-07-15 05:46:13 PDT ---
When used with a range that supports slicing, take(r, n) returns r[0..n], which
unfortunately makes it impossible to declare a variable of type Take!R and have
it work in all situations.
I do consider this a bug and not an intended part of the design, please correct
me if this is not the case.

eg.
int[] a;
Take!R r = take(a, 3); // type mismatch error

In most situations this is not a problem as type inference can be used, but
when the type need to be known (as in a struct declaration) it won't work.
Because take is an auto function, typeof(take(r, n)) does not work either.

To fix this without disabling the slicing optimisation:

1. Change the template constraint on 'Take'

-  struct Take(R) if (isInputRange!(R))
+  struct Take(R) if (isInputRange!(R) && !hasSlicing!R)

2. Add a template to handle the other case

+  template Take(R) if (isInputRange!R && hasSlicing!R)
+  {
+     alias typeof(R.init[0..R.init.length]) Take;
+  };

3. Change the return type of take from 'auto' to 'Take!R'

-  auto take(R)(R input, size_t n) if (isInputRange!R && hasSlicing!R)
+  Take!R take(R)(R input, size_t n) if (isInputRange!R && hasSlicing!R)

With these changes take and Take work properly with everything. I _will_ learn how to make real diffs one day.

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David Simcha <dsimcha@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |dsimcha@yahoo.com
         Resolution|                            |FIXED


--- Comment #1 from David Simcha <dsimcha@yahoo.com> 2010-08-16 16:51:43 PDT ---
Fixed SVN.

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


--- Comment #2 from yebblies <yebblies@gmail.com> 2010-12-15 22:12:30 PST ---
Unfortunately this has been broken again by:
http://www.dsource.org/projects/phobos/changeset/2102
(http://d.puremagic.com/issues/show_bug.cgi?id=5052)
which added a new overload for 'take' but does not add a corresponding 'Take'
template.

Patch:

Change the template constraint on the main Take range to match the main take function, and add a 'Take' template for the Take!Take!R case.


range.d:2074
- if(isInputRange!(Unqual!Range) &&
- (!hasSlicing!(Unqual!Range) || isNarrowString!(Unqual!Range)))
+ if((isInputRange!(Unqual!Range) && (!hasSlicing!(Unqual!Range) ||
isNarrowString!(Unqual!Range)))
+     && !is (Range T == Take!T))


+ // For the simplified Take!Take!R case
+
+ template Take(R)
+ if((isInputRange!(Unqual!R) && (!hasSlicing!(Unqual!R) ||
isNarrowString!(Unqual!R)))
+    && is (R T == Take!T))
+ {
+     alias R Take;
+ }

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Lars T. Kyllingstad <bugzilla@kyllingen.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@kyllingen.net
         AssignedTo|nobody@puremagic.com        |bugzilla@kyllingen.net


--- Comment #3 from Lars T. Kyllingstad <bugzilla@kyllingen.net> 2010-12-16 01:24:12 PST ---
Since I broke it, I'll take care of fixing it as well.  (And I'll make sure to add a unittest so it doesn't break again.)  But it'll probably have to wait until 2.051 is released.

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Lars T. Kyllingstad <bugzilla@kyllingen.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED


--- Comment #4 from Lars T. Kyllingstad <bugzilla@kyllingen.net> 2011-02-14 05:49:07 PST ---
https://github.com/D-Programming-Language/phobos/commit/3948e3f61403bd7618913c36959158018970011d

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