>> objc_msgSend is written in assembly. There are two reasons for this: one is that it's not possible to write a function which preserves unknown arguments and jumps to an arbitrary function pointer in C.
> Wow... this is a bit off topic but can anyone expand on this side note and explain why?
There are some good detailed replies in this thread but I thought I'd address your question at a higher level.
People often refer to C as "an assembly language" but the usage is joking, or as an analogy. The C language has a high level representation of stack frames and the like (which, BTW, intimately reflect the architecture of the PDP-7/PDP-11 class of machines -- and thus due to the popularity of C have constrained the architecture of contemporary CPUs as well). If you want to violate C's assumptions you can't by definition do it in C. ObjC messages are essentially Smalltalk messages and they have different semantics.
You don't have to become an assembly wizard but I suggest you may enjoy reading the C ABI for your favorite processor and then write a small assembly program that constructs a stack frame and calls a C function, and write an assembly function that can be called from C.
More broadly, you may be interested in the theoretical work of programming language semantics (consider reflective languages like 2Lisp and 3Lisp, Brown etc) and consider why macros (not what C calls macros) aren't a way of trying to optimize code but actually extend language syntax. Theoretical computer science can seem arcane, yet really Gödel, Russel, et al really are applicable to machine code generation.
ObjC messages are essentially Smalltalk messages and they have different semantics.
The method bodies themselves are ordinary C functions -- you can call methodForSelector: on any object to get one of its methods as a function pointer. The only problem is passing the arguments correctly.
> Wow... this is a bit off topic but can anyone expand on this side note and explain why?
There are some good detailed replies in this thread but I thought I'd address your question at a higher level.
People often refer to C as "an assembly language" but the usage is joking, or as an analogy. The C language has a high level representation of stack frames and the like (which, BTW, intimately reflect the architecture of the PDP-7/PDP-11 class of machines -- and thus due to the popularity of C have constrained the architecture of contemporary CPUs as well). If you want to violate C's assumptions you can't by definition do it in C. ObjC messages are essentially Smalltalk messages and they have different semantics.
You don't have to become an assembly wizard but I suggest you may enjoy reading the C ABI for your favorite processor and then write a small assembly program that constructs a stack frame and calls a C function, and write an assembly function that can be called from C.
More broadly, you may be interested in the theoretical work of programming language semantics (consider reflective languages like 2Lisp and 3Lisp, Brown etc) and consider why macros (not what C calls macros) aren't a way of trying to optimize code but actually extend language syntax. Theoretical computer science can seem arcane, yet really Gödel, Russel, et al really are applicable to machine code generation.