[Caml-list] a class as method parameter...

[Caml-list] a class as method parameter...

[Michael]

Hi,

I don't understand why this doesn't work:

class one = object
  val name = "test"
  method name = name
end;;
class two = object
  method take_one o -> o#name
end;;

that gives:
Some type variables are unbound in this type:
  class two : object method take_one : < name : 'a; .. > -> 'a end
The method take_one has type (< name : 'b; .. > as 'a) -> 'b where 'a
is unbound

I have to declare:
class two = object
  method take_one : 'a. (#one as 'a) -> string = fun o ->  o#name
end;;

.. to get it work (from chapter 3.10 )

why has it to be declared this way? 
( and not:
class two = object
  method take_one ( o : #one ) =  o#name
end;;

which also does not work:
The method take_one has type (#one as 'a) -> string where 'a is unbound ) ??

thanks,
 Michael
 



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Re: [Caml-list] a class as method parameter...

[skaller]

On Fri, 2004-05-28 at 19:25, Michael wrote:
> Hi,
> 
> I don't understand why this doesn't work:
> 
> class one = object
>   val name = "test"
>   method name = name
> end;;

What kind of weirdness is this? A val called name
and also a method called name??

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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Re: [Caml-list] a class as method parameter...

[Michael]

On Freitag, 28. Mai 2004 16:33, skaller wrote:
> On Fri, 2004-05-28 at 19:25, Michael wrote:
> > Hi,
> >
> > I don't understand why this doesn't work:
> >
> > class one = object
> >   val name = "test"
> >   method name = name
> > end;;
>
> What kind of weirdness is this? A val called name
> and also a method called name??

oke, use:
class one method name = "one" end

it is just an access method to get the val back, rename it as you like :-). 
pretty useless, of course as standalone program, the whole thing, but short 
enough for my previous question:
why does this not work:

  method take_one ( o : #one ) =  o#name

(in class two...)

 Michael

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Re: [Caml-list] a class as method parameter...

[skaller]

On Sat, 2004-05-29 at 00:49, Michael wrote:
> On Freitag, 28. Mai 2004 16:33, skaller wrote:

> it is just an access method to get the val back, rename it as you like :-). 

Ya, but it makes it much harder to see the typing
issue if you have to keep thinking about which name
is being refered to .. fact is i'd never do this,
and so I had no idea how Ocaml resolved it ..

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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Re: [Caml-list] a class as method parameter...

[Remi Vanicat]

skaller <skaller@users.sourceforge.net> writes:

> On Fri, 2004-05-28 at 19:25, Michael wrote:
>> Hi,
>> 
>> I don't understand why this doesn't work:
>> 
>> class one = object
>>   val name = "test"
>>   method name = name
>> end;;
>
> What kind of weirdness is this? A val called name
> and also a method called name??

method and val don't live in the same domain name. There is no
problem in the point of vue of ocaml (and semantically, they are the
same here, so it is not too much a problem for code's users).
-- 
Rémi Vanicat

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