[mpweiher]

While inheritance is OK, and useful in programming-by-difference scenarios, Objective-C style polymorphism has always de-emphasized inheritance.

Dynamic dispatch is central to both the most productive and largest-scale software systems/environments in the world. If you think the compiler can tell you everything, you're in for a world of hurt, and if you think you can statically type-check the world: good luck.

Again, inheritance is useful, though overused in static languages that only allow polymorphism together with inheritance.

[saagarjha]

Objective-C deemphasizes formal inheritance. Class clusters and informal protocols generally substitute for some of the benefits that inheritance can give.