• Rick Mann <rmann-d-lang latencyzero.com> Mar 01 2007
• mike <vertex gmx.at> Mar 02 2007
• =?ISO-8859-15?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> Mar 02 2007
• "Jarrett Billingsley" <kb3ctd2 yahoo.com> Mar 02 2007

Rick Mann <rmann-d-lang latencyzero.com> writes:

In writing code against the Mac OS X Carbon API, I often have a need to do this:

struct __Foo {};
typedef Foo*   FooRef;
typedef FooRef     BarRef;

{
  BarRef br = ...;
  FooRef fr = ...;
  if (br == null)  {} // complain
  if (fr == null) {} ok

GDC 0.22/DMD 1.004 complains about the comparison to br: "Error: incompatible
types for ((br) == (null)): 'BarRef' and 'void*'

I can avoid it by aliasing BarRef instead of typedefing it, but I have the need
to allow a BarRef to be passed to FooRef parameters, but not the other way
around. The typedef gives me that.

mike <vertex gmx.at> writes:

Am 02.03.2007, 01:40 Uhr, schrieb Rick Mann <rmann-d-lang latencyzero.co=
m>:

 In writing code against the Mac OS X Carbon API, I often have a need t=



 do this:

 struct __Foo {};
 typedef Foo*   FooRef;
 typedef FooRef     BarRef;

 {
   BarRef br =3D ...;
   FooRef fr =3D ...;
   if (br =3D=3D null)  {} // complain
   if (fr =3D=3D null) {} ok

 GDC 0.22/DMD 1.004 complains about the comparison to br: "Error:  =


 incompatible types for ((br) =3D=3D (null)): 'BarRef' and 'void*'

 I can avoid it by aliasing BarRef instead of typedefing it, but I have=



 the need to allow a BarRef to be passed to FooRef parameters, but not =



 the other way around. The typedef gives me that.


You should always use the "is" operator to check for null:

' if (br is null) { ... }

-Mike

-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/

=?ISO-8859-15?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:

mike wrote:

 You should always use the "is" operator to check for null:
 
 ' if (br is null) { ... }


Using == is perfectly valid for pointers (such as those).

--anders

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"Rick Mann" <rmann-d-lang latencyzero.com> wrote in message 
news:es7rp3$153q$1 digitalmars.com...
 In writing code against the Mac OS X Carbon API, I often have a need to do 
 this:

 struct __Foo {};
 typedef Foo*   FooRef;
 typedef FooRef     BarRef;

 {
  BarRef br = ...;
  FooRef fr = ...;
  if (br == null)  {} // complain
  if (fr == null) {} ok

 GDC 0.22/DMD 1.004 complains about the comparison to br: "Error: 
 incompatible types for ((br) == (null)): 'BarRef' and 'void*'

 I can avoid it by aliasing BarRef instead of typedefing it, but I have the 
 need to allow a BarRef to be passed to FooRef parameters, but not the 
 other way around. The typedef gives me that.


template realType(T)
{
    static if(is(T U == typedef))
        alias realType!(U) realType;
    else
        alias T realType;
}

bool isNull(T)(T val)
{
    return (cast(realType!(T))val is null);
}

void main()
{
    BarRef br;
    FooRef fr;

    if (isNull(br)) {}
}



:S

There's got to be a better way..