Question

I am attempting to learn oCaml and am having an issue as to why the below program is invalid.

class myClass2 = object  method doSomething = Printf.printf '%s\n' 'Doing something' end;;  class myClass foo = object  val dMember = foo  method doIt = dMember#doSomething end;;  let mc2 = new myClass2;; let mc = new myClass mc2;; mc#doIt;; 

The error I receive when trying to compile the program is:

File 'sample.ml', line 6, characters 5-84: Some type variables are unbound in this type:   class myClass :     (< doSomething : 'b; .. > as 'a) ->     object val dMember : 'a method doIt : 'b end The method doIt has type 'a where 'a is unbound 

I am particularly interested as to why:

val dMember = foo method doIt = dMember#doSomething 

is invalid. Any (and I mean any) help is appreciated.

Answer 1

Declare the type:

class myClass (foo:myClass2) =