The `NSMethodSignature' class
    The NSMethodSignature class is used to provide information for accessing
    the arguments of a method. It is initialized either with an already
    created encoding of a selector or only with its argument types.

    For example:

        id anObject;
        struct objc_method* mth = class_get_instance_method(self->isa, aSelector);
        const char* types = mth->method_types;
        id signature = [NSMethodSignature signatureWithObjCTypes:types];


    The above example shows the initialization of a NSMethodSignature object
    given the complete selector's encoding. The example below shows the
    initialization of a NSMethodSignature object giving only the method
    types. This corresponds to a method that has the return type void and
    has an integer argument.

        id signature = [NSMethodSignature signatureWithObjCTypes:"v@:i];


  Implementation notes

    For a given machine you must define the following macros:

    * CUMULATIVE_ARGS
    * INIT_CUMULATIVE_ARGS
    * FUNCTION_ARG_ENCODING

    The name of this macros are the same with the similar ones from the GNU
    CC compiler. However they don't correspond neither in semantics nor in
    the argument types.

    CUMULATIVE_ARGS is the data type of a variable used to hold about
    arguments processed so far. On a machine where all the arguments are
    passed on stack, this type is usually `int'.

    INIT_CUMULATIVE_ARGS should initialize the variable of type
    CUMULATIVE_ARGS described above.

    FUNCTION_ARG_ENCODING determines the encoding of the next argument of a
    method. It must produce a NSString describing the Objective-C encoding
    and position of the argument in the arguments frame of the method.

    If you want to determine how to write the encoding for a new machine you
    could use the program generated by signature-test.pl perl script. This
    generates a class with a lot of methods. You can look at the output of
    the program to see how the compiler encodes the methods. Also take a
    look in the objc-act.c file in the compiler to see how the methods are
    encoded.