Dynamic Dispatch

Dynamic dispatch is the mechanism by which the target of a method call is resolved at runtime rather than compile time, enabling polymorphism and runtime extensibility. In languages such as Objective-C, every method call is a message sent to a receiver, and the runtime maps the message selector to an implementation function through a lookup table. This contrasts with C++, which typically resolves virtual function calls via a virtual method table known at compile time.

Dynamic dispatch is the technical foundation of late binding, allowing objects to intercept, forward, or modify the behavior of messages they receive. The performance cost of runtime resolution is real but overstated: the flexibility it enables — runtime class loading, method swizzling, transparent proxying — has underpinned the architecture of every major Apple framework for three decades. Static dispatch optimizes for execution speed; dynamic dispatch optimizes for system evolution speed. The choice between them is a bet on whether the system is more likely to change than to execute.