no property 'opCall' for type ... what am I doing wrong?

[Daniel Keep]

Chad J wrote:
> Myron Alexander wrote:
>> Chad J wrote:
>>
>>> main.d:
>>> import std.stdio;
>>>
>>> struct A
>>> {
>>>   int member1;
>>> }
>>>
>>> struct B
>>> {
>>>   int member2;
>>> }
>>>
>>> void main()
>>> {
>>>   A a;
>>>   writefln( (cast(B)a).member2 );
>>> }
>>>
>>> That code results in the following compiletime errors:
>>> main.d(16): Error: no property 'opCall' for type 'B'
>>> main.d(16): Error: function expected before (), not 1 of type int
>>> main.d(16): Error: no property 'member2' for type 'int'
>>>
>>> I am using DMD 1.014 on Windows.
>>> This seemed to work at some point in history, but not anymore.  What
>>> am I doing wrong?
>>>
>>> Thanks
>>
>>
>> Chad,
>>
>> What you are doing there is illegal code. The structs A and B are
>> distinct types and cannot be cast to each other. If it worked in the
>> past, then it was probably a compiler bug.
>>
>> Since structs do not allow for inheritance (they are value types),
>> then the only way would be to use classes and inheritance or templates.
>>
>> What are you trying to achieve? Perhaps I can try to suggest a
>> different method.
>>
>> Regards,
>>
>> Myron.
> 
> Ah, makes sense.  I figured out what I was doing wrong in the original
> code.  Thanks.

This works:

void main()
{
  A a;
  writefln( (cast(B*)&a).member2 );
}

Just keep in mind that you can't take the address of a function
argument, so if you do this inside a function, you have to make a copy
first.  I've used this trick to do all sorts of evil things like turn a
structure into a ubyte[] :P

	-- Daniel

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

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