http://d.puremagic.com/issues/show_bug.cgi?id=7637

           Summary: writeln doesn't take custom toString into account
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrej.mitrovich@gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2012-03-03 17:11:49 PST ---
import std.stdio;

struct Foo {
    string toString(bool x) { return ""; }
}

void main()
{
    Foo foo;
    writeln(foo.toString());  // nogo: ok
    writeln(foo);  // compiles
}

The second writeln() call shouldn't compile. It seems writeln uses a default
toString if it doesn't find a toString() function that takes exactly zero
arguments.

Note that it will call the custom toString if 'x' has a default argument.

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SomeDude <lovelydear@mailmetrash.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lovelydear@mailmetrash.com


--- Comment #1 from SomeDude <lovelydear@mailmetrash.com> 2012-04-19 09:46:20 PDT ---
The above code doesn't compile on 2.059 Win32.

However this compiles:

import std.stdio;

struct Foo {
    string toString(bool x) { return ""; }
}

void main()
{
    Foo foo;
    writeln(foo.toString(true));  // nogo: ok
    writeln(foo);  // compiles
}



PS E:\DigitalMars\dmd2\samples> rdmd bug.d
toto
Foo()

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--- Comment #2 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2012-04-19 10:11:26 PDT ---
(In reply to comment #1)
> The above code doesn't compile on 2.059 Win32.

nogo in a comment means that line doesn't compile. The second call is the interesting one.

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--- Comment #3 from Kenji Hara <k.hara.pg@gmail.com> 2012-04-20 03:11:31 PDT ---
This is current std.format design, not accepts-invalid bug.

Today, std.format.formatValue (it is internally used by writeln and writefln) only supports following toString specializations:

http://dlang.org/phobos/std_format.html
----
const void toString(scope void delegate(const(char)[]) sink, FormatSpec fmt);
const void toString(scope void delegate(const(char)[]) sink, string fmt);
const void toString(scope void delegate(const(char)[]) sink);
const string toString();

If there is no toString() that matches required signatures, formatValue formats the object with 'TypeName(field-formattings-separeted-with-comma)', instead of reporting 'invalid toString signature detected' error.

There is two design decides:
- Ignoring invalid toString makes more user-defined types formattable.
- Shouldn't prevent any kind of toString that user really wants.

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

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


--- Comment #4 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2012-04-20 09:19:13 PDT ---
Ok fair enough.

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