about OO, from Practical Clojure June 23, 2010

http://zmila.livejournal.com/663447.html

Practical Clojure (By Luke VanderHart and Stuart Sierra)

Pure functions lead to a high degree of code encapsulation and reusability. Each function is effectively a black box. Therefore, understand the inputs and the outputs, and you understand the function. There's no need to know or care about the implementation. Object-oriented languages try to achieve this with objects, but actually it is impossible to guarantee, because objects have their own state. An object’s type and method signatures can never tell the whole story; programmers also have to account for how it manages its state and how its methods impact that state. In a complex system, this quickly grows in complexity and often the advantages of class encapsulation quickly disappear. A pure function, however, is guaranteed to be entirely described by its interface—no extra knowledge required.

Object-Oriented Programming It doesn't really solve the problems of code abstraction and modularization. It is just as easy to write over-dependent “spaghetti” code in an object-oriented language as any other. It still takes skill and special effort to write code that can truly be used without problems in a variety of environments.

It encourages a high degree of ceremony and code bloat. Simple functionality in Java can require several interdependent classes. Efforts to reduce close coupling through techniques like dependency injection involve even more unnecessary interfaces, configuration files, and code generation. Most of the bulk of a program is not actual program code, but defining elaborate structures to support it.