Objective-C Programming: The Big Nerd Ranch Guide

Dynamic method lookup and execution

A running Objective-C application consists largely of objects sending messages to each other. When an object sends a message, it kicks off a search for the method to execute. The search normally starts with the class referenced by the receiver’s isa pointer and then proceeds up the inheritance hierarchy until it finds a method of that name.

The dynamic search and the execution of the found method make up the basis of every Objective-C message send and are another feature of the Runtime.

Performing this lookup and executing the method is the job of the C function objc_msgSend(). This function’s arguments are the receiver of the message, the selector of the method to be executed, and any arguments ...