From: ES <ruby-ml@...>
Date: 2005-03-14T04:48:41+09:00
Subject: Re: how do you duck-type something to String, so String believes you?


On 3/13/2005, "Navindra Umanee" <navindra@cs.mcgill.ca> wrote:
>> What you can do is override String.== to take this into consideration.
>>
>> class String
>>         alias :_equals :==
>>         def ==(o)
>>                 _equals(o.to_s)
>>         end
>> end
>
>ES is right, you don't need to redefine == in String if you do it in
>Str.  I didn't notice that str1 and str2 were swapped around in the
>call to rb_equal.
>
>    if (TYPE(str2) != T_STRING) {
>        if (!rb_respond_to(str2, rb_intern("to_str"))) {
>            return Qfalse;
>        }
>        return rb_equal(str2, str1);
>    }
>
>Clever.  :-)

Possibly a bit too clever. While I like the reversal of roles in this
fashion to facilitate the current implementation, I'm somewhat leery
of the concept.

First of all, an *single* explicit method is used, not the representative
API of the class; for example in this instance, anything that defines
#to_s
could be considered to be valid input; sometimes more matching methods
might be required. It is considerably harder to construct the idiom this
way, so I can see the need for this compromise.

Secondly, the naming is confusing. #to_str? str is not a class and a very
similar name #to_s does something different. A better choice would use the
entire class name (lowercase would be fine) and clearly indicate that
it's
not necessarily being made into another class but used as an instance of
the other class; hence SomeClass#as_string or something similar like my
favourite SomeClass#quack_like_a_string.

I think this is being changed somehow in 2.0, even if it's just better
integration and clearer guidelines for usage.

>Cheers,
>Navin.

E