http://d.puremagic.com/issues/show_bug.cgi?id=5042

           Summary: format("%s") of struct without toString
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-10-11 15:18:36 PDT ---
Given a plain struct like Foo, the to!string creates a good enough textual representation of it:


import std.conv: to;
struct Foo { int x; }
void main() {
    assert(to!string(Foo(1)) == "Foo(1)");
}



A nomal writefln("%s") just prints "Foo":


import std.stdio: writeln, writefln;
struct Foo { int x; }
void main() {
    writeln(Foo(1)); // ==> Foo
    writefln("%s", Foo(1)); // ==> Foo
}



But the format("%s") doesn't work:


import std.string: format;
struct Foo { int x; }
void main() {
    assert(format("%s", Foo(1)) == "Foo(1)");
}


DMD 2.049 gives the error:
std.format.FormatError: std.format Can't convert test.Point to string: "string
toString()" not defined


I expect this format("%s") to return "Foo(1)" or "Foo" (I prefer "Foo(1)").

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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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SomeDude <lovelydear@mailmetrash.com> changed:

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


--- Comment #1 from SomeDude <lovelydear@mailmetrash.com> 2012-04-22 09:13:12 PDT ---
I don't know if the bug is that std.string.format doesn't work on everything or if it's the sketchy documentation, "Format arguments into a string.", which implies that it should work on everything without further explanations.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |DUPLICATE


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2012-04-22 17:36:58 PDT ---
*** This issue has been marked as a duplicate of issue 6595 ***

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--- Comment #3 from bearophile_hugs@eml.cc 2012-04-24 18:42:50 PDT ---
In dmd 2.060alpha:


import std.stdio: writeln, writefln;
import std.string: format;
struct Foo { int x; }
void main() {
    writeln(Foo(1)); // ==> Foo(1)
    writefln("%s", Foo(1)); // ==> Foo(1)
    writeln(format("%s", Foo(1))); // run-time error
}


I see this error still:

Foo(1)
Foo(1)
std.format.FormatException@std\format.d(4749): Can't convert test.Foo to
string: "string toString()" not defined


If it's isn't a problem in just my DMD, then I'll reopen this issue...

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--- Comment #4 from Kenji Hara <k.hara.pg@gmail.com> 2012-04-24 18:56:37 PDT ---
(In reply to comment #3)
> In dmd 2.060alpha:
> 
[snip]
> 
> If it's isn't a problem in just my DMD, then I'll reopen this issue...

std.string.format function only support TypeInfo based formatting.
Then it never supports raw field based, and alias this based formatting.

As discussed here: https://github.com/D-Programming-Language/phobos/pull/231

For the backward compatibility, we cannot change the implementation of std.string.format function. Instead, in 2.060head, we add a xformat function that uses std.format.formattedWrite function as the implementation.

After all, you should use std.string.xformat instead of std.string.format in 2.060 and later.

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--- Comment #5 from bearophile_hugs@eml.cc 2012-04-24 19:07:34 PDT ---
(In reply to comment #4)

> After all, you should use std.string.xformat instead of std.string.format in 2.060 and later.

Thank you Hara, this works:

import std.stdio: writeln, writefln;
import std.string: xformat;
struct Foo { int x; }
void main() {
    writeln(Foo(1)); // ==> Foo(1)
    writefln("%s", Foo(1)); // ==> Foo(1)
    writeln(xformat("%s", Foo(1))); // ==> Foo(1)
}

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