From: "David A. Black" <dblack@...>
Date: 2008-04-23T08:58:54+09:00
Subject: Re: Extending Hast class with custom [] []= methods

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Hi --

On Wed, 23 Apr 2008, I=C3=B1aki Baz Castillo wrote:

> Hi, I'd like to extend Hash class [] and []=3D methods in order to find a=
 key
> with case insensitive. This is:
>
>
> - The actual Hash [] behaviour:
>
> {"a"=3D>1,"b"=3D>2}["a"]
> =3D> 1
> {"a"=3D>1,"b"=3D>2}["A"]
> =3D> nil
>
> - The beaviour I look for:
>
> {"a"=3D>1,"b"=3D>2}["a"]
> =3D> 1
> {"a"=3D>1,"b"=3D>2}["A"]
> =3D> 1
>
>
> But I can't modify [] method since it's Ruby core written in C:
>
> ----------------------
> VALUE
> rb_hash_aref(hash, key)
>    VALUE hash, key;
> {
>    VALUE val;
>
>    if (!st_lookup(RHASH(hash)->tbl, key, &val)) {
>        return rb_funcall(hash, id_default, 1, key);
>    }
>    return val;
> }
> -----------------------
>
>
> How could I do it?

You can reopen the Hash class in Ruby, but it's not a good idea to
change the documented behavior of core methods. A better way is to
write a module, and then use it selectively for the hashes that need
it:

   module CaseInsensitiveLookup
     def [](key)

etc., and then:

   my_hash.extend(CaseInsensitiveLookup)


David

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