Slang - self primitive: parameters:

tim Rowledge tim at
Wed Dec 14 03:39:00 UTC 2005

On 13-Dec-05, at 6:03 PM, Brad Fuller wrote:

> Brad Fuller wrote:
>> Hello all,
>> I'm trying to generate a 'ulong' in Slang using the "self  
>> primitive: parameters:" method.
Don't think that is likely to work. There isn't really an unsigned  
long type in Smalltalk - the class Unsigned is only used in some of  
the strange TestOSAPlugin prims along with #asOop: which tries to  
make a valid positive 32bit  number out of it. Take a look for  
references to the class Unsigned to see what I mean.

If what you want is to extract the param and treat it as an unsigned  
long (you might also need to think about 64bitness) then you will  
need to pass in a SmallInteger or possibly a LargePositiveInteger -  
which means using Oop - and coerce it later.

>>    self primitive: 'primitivePutOutputParms'
>>        parameters: #(#SmallInteger #SmallInteger #Unsigned #Float  
>> #String).
>> But, I don't know how.  #Float generates a double and SmallInteger  
>> generates "int".  What are the other ones? Is this a dictionary?
>> When I use #Unsigned it generates:
>>    int parm2;
>>    interpreterProxy->success(interpreterProxy->isKindOf 
>> (interpreterProxy->stackValue(2), "Unsigned"));
>>    parm2 = interpreterProxy->stackValue(2);
>> which I don't think I want, do I?
Nope. It probably ought to raise an error rather than just sticking  
something meaningless in there.

>> Also, does anyone know how to generate void pointer?: (void *)?
coerce it - as in "self cCoerce: fred to: 'void *' "

> Further to add to this thread:
> I need to return a char pointer from a primitive back to Squeak,  
> but I can't find out how to do it in Slang. Can anyone give me  
> pointers?
I doubt you really want to return a char pointer; what use would it be?
If you really want to have the pointer - it is a real not-in-object- 
space pointer isn't it? - then you'd need to return it as a number  
and then do the right thing with it when you call some other prim  
that can make sense of it. For example, we pass file structure  
pointers up to Squeak from the FilePlugin and only look at them in  
If you actually want the String, then you need to create a String  
object and copy the chars from your pointer into the String instance.
Take a look at MIDIPlugin>primitiveMIDIGetPortName: where the nameObj  
is a createdString and the C call memcpy() is used to fill it.

> Using:
> self returnTypeC: 'char *'
> works great for the return of a routine, but I need the return  
> value to be pushed on the stack for return back to Squeak.
As mentioned above, you probably don't want the actual char * from  
what I can see.

> what I have is this which doesn't work quite right.. (primarily  
> because I can't quite get the whole idea of this):
> primitiveGetText
>    | text |
>    self var: #text declareC: 'char *text'.
>    self primitive: 'primitiveGetText'.
ok - note you are at liberty to name the prim anything here, "self  
primitve: 'primFred' " would work as well. You have to remember to  
actually *call* primFred of course.
>    text := self cCode: 'GetText()'.
ok - note that you can get away with replacing "self cCode:'strlen 
(fred)' " with "self strlen: fred" and it has the virtue that you can  
implement #strlen: somewhere for simulation purposes.
>    ^text asValue: String.
bad; this is not converting text into a String, it is assuming text  
is already a String object and giving you the C pointer that would be  
valid if you treat it as a string. Poor choice of name, maybe. More  
often than not you'll see the code rather more directly using  
"interpreterProxy firstIndexableField: nameOop" instead.

tim Rowledge; tim at;

More information about the Vm-dev mailing list