You can't have opaque struct pointers in the @interface, if the @implementation knows the struct

[mulle-nat]

struct opaque_struct;

@interface Foo
{
   struct opaque_struct  *p;  // will signature to ^{opaque_struct=}
}
@end


@implementation Foo

+ (Class) class
{
   return( self);
}

@end


// no longer opaque
struct opaque_struct
{
   int  foo;
};


@interface Bar
{
   struct opaque_struct  *p;  // will signature to ^{opaque_struct=i}
}
@end


@implementation Bar

+ (Class) class
{
   return( self);
}

@end

Thoughts

• this is fine (?)
• use a category to separate non-opaque knowledge
• the @encode for pointers should be opaque in all cases