https://d.puremagic.com/issues/show_bug.cgi?id=12162

           Summary: writeln(args) and writefln("%s", args) have different
                    semantics with variadic args
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrej.mitrovich@gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-02-14 12:38:46 PST ---
-----
import std.stdio;

void test(T...)(T args)
{
    writefln("%s", args);
    writeln(args);
}

void main()
{
    test(1, 2, 3, 4);
}
-----

$ dmd test.d
> 1
> 1234

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Jakob Ovrum <jakobovrum@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakobovrum@gmail.com


--- Comment #1 from Jakob Ovrum <jakobovrum@gmail.com> 2014-02-14 12:44:48 PST ---
(In reply to comment #0)
> -----
> import std.stdio;
> 
> void test(T...)(T args)
> {
>     writefln("%s", args);
>     writeln(args);
> }
> 
> void main()
> {
>     test(1, 2, 3, 4);
> }
> -----
> 
> $ dmd test.d
> > 1
> > 1234

Well, what did you expect?

I personally would've expected it to error on the basis of having received too many arguments (or was that error phased out?), but this behaviour looks correct to me.

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--- Comment #2 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-02-14 12:47:18 PST ---
(In reply to comment #1)
> Well, what did you expect?

I guess I'm looking for some kind of eager version of %s? This isn't necessarily a bug, but could be an enhancement request (unless it can already be done with another format spec?).

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--- Comment #3 from Jakob Ovrum <jakobovrum@gmail.com> 2014-02-14 12:49:06 PST ---
(In reply to comment #2)
> (In reply to comment #1)
> > Well, what did you expect?
> 
> I guess I'm looking for some kind of eager version of %s? This isn't necessarily a bug, but could be an enhancement request (unless it can already be done with another format spec?).

It would necessitate treating all trailing arguments equally (which would arguably only make sense for %s).

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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> 2014-02-14 12:52:14 PST ---
Ah I know of a cute trick though:

writefln("%s", args.only);

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--- Comment #5 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-02-14 12:53:09 PST ---
(In reply to comment #4)
> Ah I know of a cute trick though:
> 
> writefln("%s", args.only);

And come to think of it, I think bearophile has a couple of format() enhancement requests specifically for tuples.

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--- Comment #6 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-02-14 12:55:28 PST ---
(In reply to comment #5)
> (In reply to comment #4)
> > Ah I know of a cute trick though:
> > 
> > writefln("%s", args.only);
> 
> And come to think of it, I think bearophile has a couple of format() enhancement requests specifically for tuples.

Specifically, the following works for arrays but not for tuples:

writefln("%(%s %)", [1, 2]);  // prints "1 2"

Perhaps if we could modify the syntax a little bit..

writefln("%!(%s %)", TypeTuple!(1, 2));  // would print "1 2"

Disregard the TypeTuple misnomer though. :)

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--- Comment #7 from Jakob Ovrum <jakobovrum@gmail.com> 2014-02-14 12:58:29 PST ---
(In reply to comment #6)
> (In reply to comment #5)
> > (In reply to comment #4)
> > > Ah I know of a cute trick though:
> > > 
> > > writefln("%s", args.only);
> > 
> > And come to think of it, I think bearophile has a couple of format() enhancement requests specifically for tuples.
> 
> Specifically, the following works for arrays but not for tuples:
> 
> writefln("%(%s %)", [1, 2]);  // prints "1 2"
> 
> Perhaps if we could modify the syntax a little bit..
> 
> writefln("%!(%s %)", TypeTuple!(1, 2));  // would print "1 2"
> 
> Disregard the TypeTuple misnomer though. :)

It is no surprise that tuples (aka template argument list) work differently from arrays, considering their auto-expansive behaviour.

bearophile's ER pertains std.typecons.Tuple, not in-built "type tuples".

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