[phobos] Changing the semantics of std.string.format

[kenji hara]

Perfectly indeed.

We cannot also use "%( ... %)" with std.string.format.

Kenji

2011/3/3 Lars Tandle Kyllingstad <lars at kyllingen.net>:
> I've looked into issue 5687, 'std.string.format() error with "%a"'.
>
>    http://d.puremagic.com/issues/show_bug.cgi?id=5687
>
> In short, the problem is that format() calls std.format.doFormat(),
> which converts all floating-point numbers internally to 80-bit reals.
> For "%a", this is most definitely *not* what you want.
>
> I think it will be a hassle to fix doFormat(), and it looks to me as
> though it's headed for deprecation anyway, being replaced by
> formattedWrite().
>
> I say the way to go is to rewrite format() in terms of formattedWrite(),
> like this:
>
>    string format(String, Args...)(String fmt, Args args)
>        if (isSomeString!String)
>    {
>        auto app = appender!string();
>        formattedWrite(app, fmt, args);
>        return app.data;
>    }
>
> This is nice and simple, and it will make format() consistent with
> writefln().  The problem is that it is a breaking change.
>
> The biggest problem is the following, because it won't be caught at
> compile time and produces subtly different results at run time.
>
>    // before
>    assert (format("%s", 123, 456) == "123456");
>
>    // after
>    assert (format("%s", 123, 456) == "123");
>
> The following currently works, but won't compile after the change:
>
>    assert (format(123, " %a", 1.0) == "123 0x8p-3");
>    assert (format(123, 456) == "123456");
>
> I don't really think these two are a problem, though, because the first
> one is rather obscure, while the second case is now taken care of by
> std.conv.text().
>
> Does anyone object to me making this change to format()?
>
> -Lars
>
>
>
>
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