NSMethodSignature

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.