Bake a NSInvocation

invocation.m

#import <Foundation/Foundation.h>

// Wrap up a call to rangeOfCharacterFromSet:options:range: in an invocation.

// clang -g -Wall -framework Foundation -o invocation invocation.m

// Little utility to dump out a method signature.
static void printSignature (NSMethodSignature *signature) {
    NSLog (@"%ld arguments", [signature numberOfArguments]);
    for (NSUInteger i = 0; i < [signature numberOfArguments]; i++) {
        NSLog (@"%ld -> %s", i, [signature getArgumentTypeAtIndex: i]);
    }
    NSLog (@"returning %s", [signature methodReturnType]);

} // printSignature


int main (void) {
    @autoreleasepool {

        // Make a call normally

        //                                 11111111112222
        //                       012345678901234567890123
        NSString *baseString = @"Why hello there, Hoover.";
        //                            |-------------|
        NSRange randomRange = (NSRange){5, 15};
        NSCharacterSet *set = [NSCharacterSet whitespaceCharacterSet];
        NSStringCompareOptions options = NSBackwardsSearch;
        NSRange lastSpace =
            [baseString rangeOfCharacterFromSet: set
                        options: options
                        range: randomRange];
        NSLog (@"%@", NSStringFromRange(lastSpace));  // returns {16, 1}

        // Build an invocation

        NSMethodSignature *rangeSignature =
            [NSString instanceMethodSignatureForSelector:
                          @selector(rangeOfCharacterFromSet:options:range:)];
        NSInvocation *spaceFinder =
            [NSInvocation invocationWithMethodSignature: rangeSignature];

        [spaceFinder retainArguments];

        [spaceFinder setTarget: baseString];
        [spaceFinder setSelector: @selector(rangeOfCharacterFromSet:options:range:)];

        [spaceFinder setArgument: &set  atIndex: 2];  // target=0, selector=1
        [spaceFinder setArgument: &options  atIndex: 3];
        [spaceFinder setArgument: &randomRange  atIndex: 4];

        [spaceFinder invoke];
        NSRange anotherLastSpace;
        [spaceFinder getReturnValue: &anotherLastSpace];

        NSLog (@"invocation result: %@", NSStringFromRange(anotherLastSpace));
        
        // Use the invocation on another object.

        //                                   1111111111
        //                         01234567890123456789
        NSString *secondString = @"I seem to be a verb!";
        //                              |-------------|
        [spaceFinder setTarget: secondString];
        [spaceFinder invoke];
        NSRange yetAnotherLastSpace;
        [spaceFinder getReturnValue: &yetAnotherLastSpace];

        NSLog (@"I seem to be a range: %@", NSStringFromRange(yetAnotherLastSpace));
        

#if PLAYING_WITH_VARARG_METHOD
        // Varargs aren't directly supported, but I _think_ you can construct an
        // invocaton that fills in the arguments accordingly.

        char *typeEncodings;
        asprintf(&typeEncodings, "%s%s%s%s%s%s",
                 @encode(id),     // self
                 @encode(SEL),    // _cmd
                 @encode(id),     // format string
                 @encode(int),    // %d
                 @encode(char *), // %s
                 @encode(id));    // %@
        printf ("ook : %s\n", typeEncodings);

        // Invoking varargs
        NSMethodSignature *initWithFormatSignature =
            [NSMethodSignature signatureWithObjCTypes: typeEncodings];
        free (typeEncodings); // asprintf dynamically allocates.

        NSInvocation *formatInvocation =
            [NSInvocation invocationWithMethodSignature: initWithFormatSignature];
        [formatInvocation retainArguments];

        printSignature (initWithFormatSignature);

        NSString *target = [NSString alloc];  // we're deferring the init.
        NSString *formatString = @"I am %d years old, and my name is %s, %@!";

        formatInvocation.target = target;
        // crashing here - dunno if it's due to the half-alloc, or
        // class clusterage, or if I'm just doing wrong.
        formatInvocation.selector = @selector(initWithFormat:);
        
        [formatInvocation setArgument: formatString  atIndex: 2];

        int age = 4;
        [formatInvocation setArgument: &age  atIndex: 3];
        
        char *name = "bork";
        [formatInvocation setArgument: name  atIndex: 4];

        NSString *interjection = @"Groovy!";
        [formatInvocation setArgument: interjection  atIndex: 5];

        [formatInvocation invoke];
        NSString *finalString;
        [formatInvocation getReturnValue: &finalString];
        NSLog (@"please? %@", finalString);
#endif // PLAYING_WITH_VARARG_METHOD
    }

    return 0;

} // main