[djur]

The OO being addressed here is the statically-typed variant made popular by C++ and its followers. Many of the points made (classes being types, interfaces, type variables, etc.) do not apply to dynamic OO languages in the Smalltalk vein.

There's even a footnote referencing Kay-style message passing OOP, but it suggests that message passing languages are not "available today in the mainstream". There are several major OO languages today based on message passing, so I don't know how that claim is justified.

[jimbokun]

Notably Ruby and Objective C.

[tonysuper]

Objective-C is probably the saddest story of any programming language.

Absolutely fantastic libraries, incredibly easy to write high-level abstractions over very low-level C code, and completely useless outside of one platform.

I wish projects like GNUStep would get more love.