I use classes less frequently (but as Markus points out they are for the
most part much more pleasant than Java or C++ classes) so my gut feeling
is that their abilities should be subsumed in the module system (mixin
modules?) and the record system.
I think you should take a look at another currently active thread - "Feature request : Tuples vs. records". One of the red lines there is the comparison of structural versus nominal typing - classes and objects belonging to the former, and modules and records to the latter. Some say that structural typing features (objects, along with Polymorphic Variants) are an appreciated alternative to the "rigid" nominal typing of OCaml (variants, records, modules). That is why I believe that classes should exist as a separate entity (I'm not that much in favour of polymorphic variants - they weaken the type checking process too much in my opinion, and I have yet to see a good use for them), so that one can use them when one needs sharing - which records (and conventional inheritance-based object systems) don't prov!
ide.
A criticism of OOP (available at http://www.geocities.com/tablizer/oopbad.htm) addresses the issue that although conventional class systems (that is, having nominal typing, not structural) are supposed to be "nature like" (OO proponents claim that objects are more suitable to modelling things as they are in nature), they often lack the dynamic aspect of the nature, the adaptability - for example, they cannot change class, and are usually adapted to one function only, or model a functionality forcefully "adapted" to the tree-like inheritance-based structure. OCaml objects seem a great alternative for that.
The way I see things, or rather the way I dream things, is having modules simply as namespaces, having extensible records (records that have nominal subtyping - inheritance, so that parts of records can be shared - very useful in GUI implementation, in my opinion) with multiple dispatch, and having structurally typed object system, like the one in OCaml. I hope I will succeed in implementing such a system one day.
- Tom