unused variable error with objects

unused variable error with objects

[Ralph Douglass]

[-- Attachment #1: Type: text/plain, Size: 1080 bytes --]

I'm a little confused by some code that I'm trying to compile some code with
"-w Ae -warn-error Ae".

Below is an examle:

class foo = object
  method bar ~(snoo : string) = ()
end;;

let biff = new foo;;
biff#bar ~snoo:"hi";;

When I compile it (ocamlc -c -w Ae -warn-error Ae foo.ml), as expected, I
get:
File "foo.ml", line 2, characters 15-19:
Warning Z: unused variable snoo.

With labeled functions, I usually do something like ~snoo:_, but it does not
work in this exampled with methods:
---
class foo = object
  method bar ~(snoo : string):_ = ()
end;;

let biff = new foo;;
biff#bar ~snoo:"hi";;
--
ocamlc -c -w Ae -warn-error Ae foo.ml
File "foo.ml", line 2, characters 15-19:
Warning Z: unused variable snoo.

On a whim, I did the following, which surprisingly worked:

class foo = object
  method bar ~(_snoo : string) = ()
end;;

let biff = new foo;;
biff#bar ~_snoo:"hi";;

And that compiles, which confused me.  But I have to put the underbar into
the method call, which seems wrong.
Is there a solution to this?

I'm running 3.10.1, from godi.

Thanks!

-- 
Ralph

[-- Attachment #2: Type: text/html, Size: 1436 bytes --]

Re: [Caml-list] unused variable error with objects

[Julien Signoles]

> With labeled functions, I usually do something like ~snoo:_, but it does not
> work in this exampled with methods:
> ---
> class foo = object
>  method bar ~(snoo : string):_ = ()
> end;;
>
> let biff = new foo;;
> biff#bar ~snoo:"hi";;
> --
> ocamlc -c -w Ae -warn-error Ae foo.ml
> File "foo.ml", line 2, characters 15-19:
> Warning Z: unused variable snoo.
>
> On a whim, I did the following, which surprisingly worked:
>
> class foo = object
>  method bar ~(_snoo : string) = ()
> end;;
>
> let biff = new foo;;
> biff#bar ~_snoo:"hi";;
>
> And that compiles, which confused me.  But I have to put the underbar into
> the method call, which seems wrong.
> Is there a solution to this?

Try this:

class foo = object
   method bar ~snoo:(_:string) = ()
end;;
(new foo)#bar ~snoo:"hi";;

--
Julien

Re: [Caml-list] unused variable error with objects

[Jeremy Yallop]

Ralph Douglass wrote:
> With labeled functions, I usually do something like ~snoo:_, but it does 
> not work in this exampled with methods:
> ---
> class foo = object
>   method bar ~(snoo : string):_ = ()
> end;;

In this case the ':_' denotes a type annotation, using the "any-type" 
expression '_'.  You're declaring the return type of the method, as 
you'll see if you change the annotation to something incompatible with 
unit, such as

    class foo = object
      method bar ~(snoo : string):int = ()
    end

> On a whim, I did the following, which surprisingly worked:
> 
> class foo = object
>   method bar ~(_snoo : string) = ()
> end;;

This works because the "unused variables" warning is disabled for 
variables which start with an underscore.  It's a useful feature for 
normal bindings but I don't think you should use it for labels, since it 
changes the interface.

> Is there a solution to this?

I think the following is what you want:

    class foo = object
      method bar ~snoo:(_:string) = ()
    end

Jeremy.

Re: [Caml-list] unused variable error with objects

[Ralph Douglass]

[-- Attachment #1: Type: text/plain, Size: 1355 bytes --]

Great, that does indeed give me exactly what I want.  I guess I just got
confused by the type annotation syntax, and for some reason I had the order
wrong.

Thanks again!

On 3/20/08, Jeremy Yallop <jeremy.yallop@ed.ac.uk> wrote:
>
> Ralph Douglass wrote:
> > With labeled functions, I usually do something like ~snoo:_, but it does
> > not work in this exampled with methods:
> > ---
> > class foo = object
> >   method bar ~(snoo : string):_ = ()
> > end;;
>
>
> In this case the ':_' denotes a type annotation, using the "any-type"
> expression '_'.  You're declaring the return type of the method, as
> you'll see if you change the annotation to something incompatible with
> unit, such as
>
>     class foo = object
>       method bar ~(snoo : string):int = ()
>     end
>
>
> > On a whim, I did the following, which surprisingly worked:
> >
> > class foo = object
> >   method bar ~(_snoo : string) = ()
> > end;;
>
>
> This works because the "unused variables" warning is disabled for
> variables which start with an underscore.  It's a useful feature for
> normal bindings but I don't think you should use it for labels, since it
> changes the interface.
>
>
> > Is there a solution to this?
>
>
> I think the following is what you want:
>
>
>     class foo = object
>       method bar ~snoo:(_:string) = ()
>     end
>
>
> Jeremy.
>



-- 
Ralph

[-- Attachment #2: Type: text/html, Size: 2023 bytes --]