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digitalmars.D.bugs - [Issue 4880] New: [patch] std.range.put does not handle output ranges implement via opDispatch; breaks on RefAppender

reply d-bugmail puremagic.com writes:
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           Summary: [patch] std.range.put does not handle output ranges
                    implement via opDispatch; breaks on RefAppender
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: sandford jhu.edu


--- Comment #0 from Rob Jacques <sandford jhu.edu> 2010-09-17 10:14:54 PDT ---
std.range.put does not correctly introspect types which implement put via
opDispatch. This is fairly simple to fix by swapping hasMember out for a
__traits compiles test.

void put(R, E)(ref R r, E e)
{
+    static if (__traits(compiles, {return R.init.put(E.init);})  ) 
-    static if (hasMember!(R, "put") ||
-    (isPointer!R && is(pointerTarget!R == struct) &&
-     hasMember!(pointerTarget!R, "put")))
    {

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next sibling parent d-bugmail puremagic.com writes:
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David Simcha <dsimcha yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsimcha yahoo.com


--- Comment #1 from David Simcha <dsimcha yahoo.com> 2010-09-17 10:38:01 PDT ---
This is a rather problematic bug.  If we use your patch, it will break when
uniform function call syntax is fully implemented.  I guess what we need is for
hasMember to be less restrictive.  It should include opDispatch, and while
we're at it, pointers to structs.

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--- Comment #2 from Rob Jacques <sandford jhu.edu> 2010-09-17 12:33:14 PDT ---
Well half of puts' functionality is to emulate uniform function call syntax for
structs and classes: i.e. re-write put(r,e) into r.put(e). So I'd expect UFC to
break put with or without this patch.

I had thought of improving hasMembers (either the __traits or templated
version) to support opDispatch, however, I do not think that it is possible.
The problem is template constraints. Consider the highly synthetic example:

  void opDispatch(string name, T...) 
    if( name.length == T.length )  {}

Because the template constraint could be non-trivially dependent on something
more than name there's no way to check if r.opDispatch!"put" is valid without
actually evaluating r.put(e) (i.e. __traits(compiles,...))

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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Rob Jacques <sandford jhu.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #3 from Rob Jacques <sandford jhu.edu> 2012-02-14 20:49:21 PST ---
I converted the patch into a pull request:

https://github.com/D-Programming-Language/phobos/pull/433

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