On 22 Feb 2014, at 00:12, Ken Thomases <k...@codeweavers.com> wrote:
> On Feb 21, 2014, at 3:17 PM, jonat...@mugginsoft.com wrote:
>
>> So I want to be able to send the same message to any class and get an
>> appropriate void* pointer.
>
> There's no one representation of its content, so there's no way for any
> recipient of a supposed "pointer to that content" (however that might be
> obtained) to interpret the pointer.
Not so.
The pointer is ultimately passed as a vararg along with a Mono method
representation as part of a Mono method invocation.
The Mono method representation includes type info for its parameters.
Hence it can cast and deference a void* pointer appropriately.
This method is used to query C#/CLR Dictionary <TKey, TValue> for a given key
using the embedded MONO C API:
- (BOOL)containsKey:(id)key
{
BOOL containsKey = NO;
// TODO: use -confromsToProtocol?
if ([key respondsToSelector:@selector(monoObject)] && [key
respondsToSelector:@selector(monoValue)]) {
// form the method name
NSString *monoArgumentTypeName = [[DBTypeManager sharedManager]
monoArgumentTypeNameForMonoObject:[key monoObject]];
NSString *methodName = [NSString stringWithFormat:@"ContainsKey(%@)",
monoArgumentTypeName];
// invoke the method
MonoObject *monoObject = [self invokeMonoMethod:[methodName UTF8String]
withNumArgs:1, [key monoValue]];
containsKey = DB_UNBOX_BOOLEAN(monoObject);
} else {
[NSException raise:@"Invalid key" format:@"Key %@ must respond to
-monoObject and -monoValue", key];
}
return containsKey;
}
- (MonoObject *)invokeMonoMethod:(const char *)methodName
withNumArgs:(int)numArgs, ... {
va_list va_args;
va_start(va_args, numArgs);
MonoObject *ret = DBMonoObjectInvoke(_monoObj, methodName, numArgs,
va_args);
va_end(va_args);
return ret;
}
In the above if key is an NSNumber containing a 5 then [key monoValue] returns
a pointer to a 5.
If the key is an NSString then [key monoValue] returns a pointer to a
monoObject representing the string.
>
> If you have some specific representation in mind, then don't use NSNumber.
> Use a custom class wrapping the specific representation you want to use.
The custom class would simply be a dupe of NSNUmber + 1 method.
My original category solution seems simpler.
>
>
>> This usage pattern, within a generated code environment too, makes the
>> imposition of an lvalue that I can take an address from undesirable.
>
> However undesirable it may be, it's a consequence of you wanting an address
> for things which don't have an address. The thing has to be stored, at least
> temporarily, in storage which has a proper address (and a predictable size
> and semantic interpretation).
This is what the code in my OP does.
>
>> Plus it also needs to be an NSNumber, not a custom NSObject subclass.
>
> Why?
I am not in control of the types on which I have to operate.
>
> If you really, really want to try to do this _and_ you can pick a single
> in-memory representation for all NSNumber content values, you could do
> something similar to what NSString does for -UTF8String. You'll notice that
> that method's returned string has the lifetime of an autoreleased object, not
> the original string object. I believe that it just creates an autoreleased
> NSData holding the UTF-8-encoded bytes and returns that NSData's -bytes. So,
> you'd do something like:
I think the code in the OP does this.
Thanks for looking
Jonathan
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