Looks like bug.
dchar[] and wchar[] format strings support less specifiers than char[]

        import std.format;
        string test1 = "%02d".format(1); // works
        assert(test1 == "01");
        dstring test2 = "%d"d.format(1); // works
        assert(test2 == "1"d);
        wstring test3 = "%02d"w.format(1); // fails
        assert(test3 == "01"w);
        dstring test4 = "%02d"d.format(1); // fails
        assert(test4 == "01"d);

On Wednesday, 9 November 2016 at 08:21:53 UTC, Vadim Lopatin wrote:
> Looks like bug.
> dchar[] and wchar[] format strings support less specifiers than char[]
>
>         import std.format;
>         string test1 = "%02d".format(1); // works
>         assert(test1 == "01");
>         dstring test2 = "%d"d.format(1); // works
>         assert(test2 == "1"d);
>         wstring test3 = "%02d"w.format(1); // fails
>         assert(test3 == "01"w);
>         dstring test4 = "%02d"d.format(1); // fails
>         assert(test4 == "01"d);

dmd 2.072.0

On 11/09/2016 12:21 AM, Vadim Lopatin wrote:
> Looks like bug.
> dchar[] and wchar[] format strings support less specifiers than char[]
>
>         import std.format;
>         string test1 = "%02d".format(1); // works
>         assert(test1 == "01");
>         dstring test2 = "%d"d.format(1); // works
>         assert(test2 == "1"d);
>         wstring test3 = "%02d"w.format(1); // fails
>         assert(test3 == "01"w);
>         dstring test4 = "%02d"d.format(1); // fails
>         assert(test4 == "01"d);
>

It's a bug that std.format uses arrayPtrDiff() here:

  https://github.com/dlang/phobos/blob/master/std/format.d#L993

arrayPtrDiff() is at the bottom of the same file but works correctly only for char strings:

  https://github.com/dlang/phobos/blob/master/std/format.d#L6573

Please report it.

Ali

On 11/09/2016 01:20 AM, Ali Çehreli wrote:

> arrayPtrDiff() is at the bottom of the same file but works correctly
> only for char strings:
>
>   https://github.com/dlang/phobos/blob/master/std/format.d#L6573

What I meant is, using arrayPtrDiff() is correct only for char strings. Otherwise, arrayPtrDiff() is working properly.

Ali