From: Robert Klemme <shortcutter@...>
Date: 2007-02-08T07:10:09+09:00
Subject: Re: Defining <<

On 07.02.2007 22:58, Gary Wright wrote:
> 
> On Feb 7, 2007, at 4:46 PM, Luke Ivers wrote:
> 
>> I'm not 100% how exactly to search to find out if someone else has posed
>> this question, but why does the following happen?
>>
>> Given:
>>
>> class Hash
>>   def << (key, val=nil)
>>     self.store(key, val)
>>   end
>> end
>>
>> h = {}
>> h << 'test'
>> h << 'test', 'bob'
> 
> The syntax rules for the << operator don't allow it to take multiple
> arguments when called via infix notation:
> 
>   h << arg1     # one argument only
> 
> you can call the method with multiple arguments but you've got to do it 
> like:
> 
>   h.<<(arg1, arg2)    # dot-style method invocation
> 
> You can use an array to 'cheat':
> 
>  h << [arg1, arg2]
> 
> But the method will only see one argument, an array, and you would have
> to expect that and/or test for it in your definition for Hash#<<.

Here's another variant:

class Hash
   Proxy = Struct.new :parent, :key do
     def <<(val)
       parent[key] = val
       parent
     end
   end
   def <<(key)
     Proxy.new self, key
   end
end

irb(main):012:0> h ={}
=> {}
irb(main):013:0> h << "foo" << "bar" << "key" << 234
=> {"foo"=>"bar", "key"=>234}
irb(main):014:0> h << 2 << 3
=> {2=>3, "foo"=>"bar", "key"=>234}
irb(main):015:0> h
=> {2=>3, "foo"=>"bar", "key"=>234}

Not that I would recommend it...

Kind regards

	robert