http://d.puremagic.com/issues/show_bug.cgi?id=6231

           Summary: [patch] std.conv.to: Structs with toString and
                    isInputRange match multiple templates.
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: patch
          Severity: normal
          Priority: P3
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: sandford@jhu.edu


--- Comment #0 from Rob Jacques <sandford@jhu.edu> 2011-06-30 11:27:03 PDT ---
If a struct defines a custom toString method and satisfies isInputRange, then to!string(Struct) will match multiple toImpl templates. The solution is to add an extra template constraint to the input range toImpl to detect structs with custom toString methods.

[Line 194 in DMD 2.053]
T toImpl(T, S)(S s, in T leftBracket = "[", in T separator = ", ",
    in T rightBracket = "]")
if (isSomeString!T && !isSomeChar!(ElementType!S) &&
(isInputRange!S || isInputRange!(Unqual!S)) )

-This is the constraint to add.
&& !(is(S == struct) && is(typeof(&S.init.toString))) )

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Rob Jacques <sandford@jhu.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[patch] std.conv.to:        |[patch]
                   |Structs with toString and   |std.conv.to/std.format.:
                   |isInputRange match multiple |Structs with toString and
                   |templates.                  |isInputRange match multiple
                   |                            |templates.


--- Comment #1 from Rob Jacques <sandford@jhu.edu> 2011-06-30 12:04:07 PDT ---
std.format.formatRange also suffers from a similar problem, although in this case it is one of choosing a non-character range over the custom toString routine.

[Line 1171 in format.d in DMD 2.053]
void formatValue(Writer, T, Char)(Writer w, T val,
        ref FormatSpec!Char f)
if (isInputRange!T && !isSomeString!T

The extra condition:
&& !(is(T == struct) && is(typeof(&T.init.toString))) )

And the toString exception needs to added to Line 1474
void formatValue(Writer, T, Char)(Writer w, T val,
        ref FormatSpec!Char f)
if (is(T == struct) && (!isInputRange!T  || is(typeof(&T.init.toString))) )

By the way, I like the idea of
   void toString(void delegate(const(char)[]) sink, FormatSpec fmt);
   void toString(void delegate(const(char)[]) sink, string fmt);
but are which one is preferred? And if/when is Object going to switch over?

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Kenji Hara <k.hara.pg@gmail.com> changed:

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


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2012-06-14 02:38:46 PDT ---
Now almost bugs around formatting were fixed.

(In reply to comment #1)
> By the way, I like the idea of
>    void toString(void delegate(const(char)[]) sink, FormatSpec fmt);
>    void toString(void delegate(const(char)[]) sink, string fmt);
> but are which one is preferred? And if/when is Object going to switch over?

Getting FormatSpec version is most specialized than others, so is preferred. And such enhanced toStrings are priority than Object.toString() in class.

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