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digitalmars.D.bugs - [Issue 8766] New: unexpected compile-time error when switching a struct definition to a class

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8766

           Summary: unexpected compile-time error when switching a struct
                    definition to a class
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: blooh_ hotmail.com


--- Comment #0 from Christopher Crouzet <blooh_ hotmail.com> 2012-10-05
20:01:04 PDT ---
Please consider the code below:

// ------------------------------
enum Storage : int
{
  dynamic = 0
}

enum StorageOrder : int
{
  columnMajor = 0,
  rowMajor = 1
}
alias StorageOrder.columnMajor defaultStorageOrder;


class Array( T_scalar, T_args ... )
{
  alias ArrayTraits!( T_scalar, T_args ) traits;
}


struct ArrayTraits( T_scalar, T_args ... )
{
  static if ( hasFlag( Flags.storageOrder ) == true )
    alias T_args[0 .. $ - 1] shapeTuple;
  else
    alias T_args shapeTuple;

  static immutable StorageOrder storageOrder = hasFlag( Flags.storageOrder ) ?
      T_args[$ - 1] : defaultStorageOrder;


  static int getFlags()
  {
    int flags = 0;
    if ( is( typeof( T_args[$ - 1] ) == StorageOrder ) )
      flags |= Flags.storageOrder;

    return flags;
  }

  static bool hasFlag( Flags flag )
  {
    return (getFlags() & flag) != 0;
  }


  enum Flags : int
  {
    dynamic = 1 << 0,
    storageOrder = 1 << 1
  }
}


void main()
{
  auto array1d = new Array!( float, 3 );
}
// ------------------------------

It all compiles fine as it is and produce the expected results.

Now, if you declare ArrayTraits as a class rather than a struct, then the
compilation fails saying that the variable 'flag' cannot be read at compile
time. I might be wrong, but when comparing the specs of classes and structs
from the doc below, I don't see anything that would explain this error
happenning only in one case but not the other?
http://dlang.org/struct.html

Also, if you keep it declared as a class but this time define the hasFlag()
arguments at conpile-time, such as 
static bool hasFlag( Flags flag )()
and adequately replace the calls to this method, then it compiles fine. I'm
getting confused here and am not sure anymore if how I initially declared it is
valid or not?

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8766


Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru


--- Comment #1 from Maxim Fomin <maxim maxim-fomin.ru> 2012-10-06 02:33:37 PDT
---
Reduced http://dpaste.dzfl.pl/348de450

If integer constant 1 is replaced by any of StorageOrder enumeration, the bug
goes away. Also if empty static if statement is cut off completely, the bug
also goes away.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #2 from bearophile_hugs eml.cc 2012-10-06 03:20:29 PDT ---
(In reply to comment #1)

 Reduced http://dpaste.dzfl.pl/348de450


Note that enums in D don't need a final semicolon. And it's better to paste or
attach the test cases in Bugzilla itself, instead of linking an external paste
site.

-----------------------

A little reduced:


enum Foo { X }
class Bar {
    static if (spam(Foo.X)) {}
    static Foo a = spam(Foo.X) ? 1 : Foo.X;
    static bool spam(Foo flag) {
        return flag != 0;
    }
}
void main() {}

DMD 2.061alpha gives:

temp.d(6): Error: variable flag cannot be read at compile time
temp.d(4):        called from here: spam(cast(Foo)0)

Replacing class with struct the error goes away.

-----------------------

Also this makes the error go away, showing it's related to a forward reference
error:

enum Foo { X }
class Bar {
    static bool spam(Foo flag) {
        return flag != 0;
    }
    static if (spam(Foo.X)) {}
    static Foo a = spam(Foo.X) ? 1 : Foo.X;
}
void main() {}

-----------------------

While this:

enum Foo { X }
class Bar {
    static if (spam(Foo.X)) {}
    static Foo a = spam(Foo.X) ? 1 : Foo.X;
    static bool spam(Foo flag) {
        return true;
    }
}
void main() {}


Gives:

temp.d(4): Error: cannot implicitly convert expression (1) of type int to Foo

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--- Comment #3 from Maxim Fomin <maxim maxim-fomin.ru> 2012-10-06 04:02:43 PDT
---
(In reply to comment #2)

 (In reply to comment #1)

 Reduced http://dpaste.dzfl.pl/348de450


 
 And it's better to paste or
 attach the test cases in Bugzilla itself, instead of linking an external paste
 site.


Dpaste is more convenient and it is supposed to be "D community" resource
rather some external paste site. The only problem I can see is that it can be
shut down when it's content is required. Is dpaste considered as very
unreliable or does often experience problems? I faced it only once.

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com


--- Comment #4 from Walter Bright <bugzilla digitalmars.com> 2012-10-06
05:08:43 PDT ---
Please paste source code reproducing a bug inline here, or attach as a file to
the bugzilla issue.

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--- Comment #5 from Maxim Fomin <maxim maxim-fomin.ru> 2012-10-06 05:47:03 PDT
---
(In reply to comment #4)

 Please paste source code reproducing a bug inline here, or attach as a file to
 the bugzilla issue.


OK

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