[dragonwriter]

> The way OOP is taught often doesn't bring up object thinking. But if you believe it is not natural, try thinking mathematically (without nouns or names as unique aliasable identifiers). Or without isa or hasa relationships.

Is-a and Has-a relationships don't require class-based OO structures to express in a language. E.g., both membership in a abstract group sharing a common interface (is-a) and composition (has-a) relationships are readily expressed in FP languages like Haskell quite directly, or in languages that are more like traditional OO langauges but which separate interface from implementation rather than combining them as is done in class-based OO.

The OO approach to programming, and thinking about domains, has broad utility, but the particulars of static, class-based OOP are not necessary to realize that utility.

[seanmcdirmid]

> but the particulars of static, class-based OOP are not necessary to realize that utility.

The design goal of a OOPL is to support object thinking. FPL generally have other goals, and some of their design philosophies reject object thinking altogether. You'll often see lots of objects in ML or Scheme libraries; but the languages are not really optimized for this way of solving problems.

Haskell, as a real pure FPL, is really the anti-thesis of object thinking. You cannot express nominal is-a relationships in Haskell very easily at all: it is all structural (and type classes don't get around that) and supports equational rather than name-based reasoning. You could add names to Haskell via GUIDs or impure language features. This is not really the way to program in Haskell, however.

[dragonwriter]

> The design goal of a OOPL is to support object thinking.

Yes, my point is that class-based OOPLs aren't the only way to do that (and in some respects create some unnecessary problems with that), which is among the reasons that many newer languages -- even ones that are not particularly functional languages, and which have OO roots -- are not class-based.

[seanmcdirmid]

A "class" is quite useful to programmers vs. some of the alternatives; even JavaScript is (syntactically at least) moving away from prototypes to having real class constructs. I prefer traits (the mixin-like scala kind, not the field-free smalltalk kind), which are basically classes enhanced with linearized multiple inheritance. There are also Beta-style virtual classes, which are quite useful, and there are even languages that support dynamic inheritance (via prototypes, predicates, or on demand).

The OOPL design space is huge. I wish there was more activity there, but all the new hot languages either do little to innovate on OO constructs, or emphasize the functional (or worse: try to push type classes as OO).