comparing typedefed type to null

[mike]

Am 02.03.2007, 01:40 Uhr, schrieb Rick Mann <rmann-d-lang at latencyzero.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.

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

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

-Mike

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