On Aug 10, 2005, at 6:02 PM, Nathaniel Gray wrote:
Is there any way to send float or double arguments to a method
designated at runtime? I've tried using objc_msgSendv, casting it
in various ways, and using -performv::, but nothing works.
Using objc_msgSendv() properly requires knowledge of your
platform's ABI. In particular, floating-point values must be stored
in a special place in the marg_list on PowerPC. objc-msg-ppc.s
notes some of the details.
I think those details are pretty well hidden by the marg_* macros
though. I've used method_getArgumentInfo() to get the offset of the
argument, and marg_setValue() to set it before calling objc_msgSendv
(). It worked fine with all sorts of types, including floats and
doubles.
* using NSInvocation. It shields you from the ABI details.
Very nice option. Definitely the best way to go, if it's flexible
enough for your needs.
* using objc_msgSend() or objc_msgSend_stret() directly. Cast
objc_msgSend() to a function pointer type that matches your
method's signature, then make the call.
Typecasting only works for that if the signature is known at compile-
time. If you won't know the signature until runtime, you'll need to
either use the marg_* macros and pass the resulting marg_list struct
to objc_msgSendv(). Or, use ffi or ffcall to call objc_msgSend().
That last option (ffi/ffcall) is the most complex, but it's the only
way I've found to implement a "foreign" language (Perl in my case)
subclass of an Objective-C class, and allow the "foreign" language to
call super's methods.
The problem I found was that there's no "v" (at least none that's
documented) equivalent to the objc_msgSendSuper() function. What I
settled on doing was using ffcall to call the "normal" msgSendSuper
functions, rather than the marg_* macros and the "v" functions.
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