http://d.puremagic.com/issues/show_bug.cgi?id=8040

           Summary: writeln(null) too
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            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 2012-05-04 12:55:24 PDT ---
Problem found by Ali Çehreli.

D2 code:


import std.stdio: writeln;
class Foo {}
struct Bar {}
void main() {
    Foo f = null;
    writeln(f);
    Bar* b = null;
    writeln(b);
    writeln(null);
}


Expected output similar to:

cast(Foo)null
cast(Bar*)null
null


DMD 2.056 prints "null" in the first two writeln, and gives errors for the third one:

...\dmd2\src\phobos\std\stdio.d(1562): Error: undefined identifier 'length'
...\dmd2\src\phobos\std\stdio.d(1562): Error: undefined identifier 'ptr', did
you mean 'template tr(C1,C2,C3,C4 = immutable(char))'?
test.d(9): Error: template instance std.stdio.writeln!(typeof(null)) error
instantiating

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2012-05-22 21:14:26 PDT ---
https://github.com/D-Programming-Language/phobos/pull/599

With my pull, original code output is:
----
null
null
null

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--- Comment #2 from bearophile_hugs@eml.cc 2012-05-23 03:01:57 PDT ---
(In reply to comment #1)
> https://github.com/D-Programming-Language/phobos/pull/599
> 
> With my pull, original code output is:
> ----
> null
> null
> null

Thank you Kenji Hara, this is an improvement.

But isn't it better to add types (as in cast(Foo) or cast(Bar*)) to better tell
apart the three kinds of null in that example?

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--- Comment #3 from Kenji Hara <k.hara.pg@gmail.com> 2012-05-23 03:26:04 PDT ---
(In reply to comment #2)
> (In reply to comment #1)
> But isn't it better to add types (as in cast(Foo) or cast(Bar*)) to better tell
> apart the three kinds of null in that example?

No, it isn't. It is consistent with other literal formatting.

writeln(1);  // prints "1", not "cast(int)1"
writeln(1L); // prints "1", not "cast(long)1"
writeln(1f); // prints "1", not "cast(float)1"

And, formatting as like cast syntax will make unfomatting complicate. It is less benefit.

Furthermore, std.format module does not print value type in general. (Deprecated typedef value was formatted like cast syntax, but I think it is special case)

Therefore, I think your proposal has many faults than benefits.

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--- Comment #4 from bearophile_hugs@eml.cc 2012-05-23 04:07:37 PDT ---
(In reply to comment #3)

> writeln(1);  // prints "1", not "cast(int)1"
> writeln(1L); // prints "1", not "cast(long)1"
> writeln(1f); // prints "1", not "cast(float)1"

In my opinion writeln(1f) and writeln(1.0L) should print 1.0, as in Python:

>>> int(1)
1
>>> float(1)
1.0


> And, formatting as like cast syntax will make unfomatting complicate. It is less benefit.
> 
> Furthermore, std.format module does not print value type in general. (Deprecated typedef value was formatted like cast syntax, but I think it is special case)
> 
> Therefore, I think your proposal has many faults than benefits.

OK. Thank you for the answers.

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--- Comment #5 from Kenji Hara <k.hara.pg@gmail.com> 2012-05-29 00:55:57 PDT ---
*** Issue 7866 has been marked as a duplicate of this issue. ***

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

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


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