Re: [Caml-list] Re: Smells like duck-typing

[Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>]

From: "William D. Neumann" <wneumann@cs.unm.edu>
> On Thu, 18 Oct 2007 18:13:05 +0200, Zheng Li wrote
> 
> > Strangely though, there seems to be a bug in the OO type system: 
> > (The solution proposed above is safe, as it does coercion)
> > 
> > # let coredump = object inherit templt end;;
> > val coredump : templt = <obj>
> > # coredump#title;;
> > 
> > Process caml-toplevel segmentation fault
> 
> Hmmm... interesting.  You can apparently create immediate objects with 
> virtual instance variables, so long as you don't have virtual methods.
> 
> Objective Caml version 3.10.0
> 
> # let bad = object method virtual ooops : int end;;
> Characters 10-47:
>   let bad = object method virtual ooops : int end;;
>             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This class should be virtual. The following methods are undefined : ooops
> # let bad_int = object val virtual x : int method get_x = x end;;
> val bad_int : < get_x : int > = <obj>
> # let bad_str = object val virtual x : string method get_x = x end;;
> val bad_str : < get_x : string > = <obj>
> # bad_int # get_x;;
> - : int = 0
> # bad_str # get_x;;

Virtual fields are a new and experimental feature in 3.10.
The above bug was fixed shortly after the release.

Jacques Garrigue