Data commit

Task/Respond-to-an-unknown-method-call/Objective-C/respond-to-an-unknown-method-call.m

@@ -0,0 +1,62 @@
+#include <Foundation/Foundation.h>
+
+// The methods need to be declared somewhere
+@interface Dummy : NSObject
+- (void)grill;
+- (void)ding:(NSString *)s;
+@end
+
+@interface Example : NSObject
+- (void)foo;
+- (void)bar;
+@end
+
+@implementation Example
+- (void)foo {
+  NSLog(@"this is foo");
+}
+
+- (void)bar {
+  NSLog(@"this is bar");
+}
+
+- (void)forwardInvocation:(NSInvocation *)inv {
+  NSLog(@"tried to handle unknown method %@", NSStringFromSelector([inv selector]));
+  NSUInteger n = [[inv methodSignature] numberOfArguments];
+  for (NSUInteger i = 0; i < n-2; i++) { // First two arguments are the object and selector.
+    id __unsafe_unretained arg;          // We assume that all arguments are objects.
+                                         // getArguments: is type-agnostic and does not perform memory management,
+                                         //   therefore we must pass it a pointer to an unretained type
+    [inv getArgument:&arg atIndex:i+2];
+    NSLog(@"argument #%lu: %@", i, arg);
+  }
+}
+
+// forwardInvocation: does not work without methodSignatureForSelector:
+// The runtime uses the signature returned here to construct the invocation.
+- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
+  int numArgs = [[NSStringFromSelector(aSelector) componentsSeparatedByString:@":"] count] - 1;
+  // we assume that all arguments are objects
+  // The type encoding is "v@:@@@...", where "v" is the return type, void
+  // "@" is the receiver, object type; ":" is the selector of the current method;
+  // and each "@" after corresponds to an object argument
+  return [NSMethodSignature signatureWithObjCTypes:
+          [[@"v@:" stringByPaddingToLength:numArgs+3 withString:@"@" startingAtIndex:0] UTF8String]];
+}
+@end
+
+int main()
+{
+  @autoreleasepool {
+
+    id example = [[Example alloc] init];
+
+    [example foo];          // prints "this is foo"
+    [example bar];          // prints "this is bar"
+    [example grill];        // prints "tried to handle unknown method grill"
+    [example ding:@"dong"]; // prints "tried to handle unknown method ding:"
+                            // prints "argument #0: dong"
+
+  }
+  return 0;
+}