From: Richard Kilmer <rich@...>
Date: 2004-06-08T02:36:20+09:00
Subject: Re: How to ducktype a Hash?




On 6/7/04 12:10 PM, "David A. Black" <dblack@wobblini.net> wrote:

> Hi --
> 
> On Tue, 8 Jun 2004, Richard Kilmer wrote:
> 
>> Moreover, if you could do that syntactically (ie. Change Ruby to support
>> this kind of thing) like the following (love it or hate it) syntax:
>> 
>> class Foo
>> 
>>   def {Hash}[](key)
>>     @mymap[key]
>>   end
>> 
>>   def {Hash}[]=(key, value)
>>     @mymap[key] = value
>>   end
>> 
>> end
>> 
>> f = Foo.new
>> f{Hash}['name']="rich"
>> 
>> ...but you don't always need the {...}
>> 
>> p f['name'] => 'rich'
>> 
>> ...and if you do something that's naughty...
>> 
>> p f{Array}[1] => raise Exception...
> 
> It would have to be something slightly different from that, though,
> because of:
> 
>   irb(main):008:0> def f; [1,2,3]; end
>   => nil
>   irb(main):009:0> f{Array}[1]
>   => 2
> 
> 
> David

Actually no...I don't think so.  Ruby's scoping handles whether something is
a method or a variable.  If its a method, then:

 p f.class => Array

 p f{Array}[1] => 2

is correct because the [] method on the Array instance is correct (by
default) in that f returns an array and you are calling:

  {Array}[1] 

On that object.  Its a question of what you are sending the message to...in
other words, the {...} is appended to the method that follows the } as
'semantic metadata', whereas with:

  f = Foo.new

  f{Array}[1]

Is sending the message to the object pointed to by the variable f.

So, where f is a variable or a method name, that is up to Ruby, but the
{Array} data is attached to the method that follows, regardless.

Its weird, because I am saying that you are kind of 'casting' the method
itself rather than the object.

-rich