From: Mike Austin <noone@...>
Date: 2006-03-12T10:23:45+09:00
Subject: Re: attribute setters for instance variables

Hans Fugal wrote:
> eliben@gmail.com wrote:
>> Hello,
>>
>> The Pickaxe book presents the following example:
>>
>> class Incorrect
>>   attr_accessor :one, :two
>>   def initialize
>>     one = 1
>>     self.two = 2
>>   end
>> end
>>
>> obj = Incorrect.new
>>
>> p obj.one
>> p obj.two
>>
>> The first thing printed is 'nil' and not '1' since "one = 1" assigns to
>> a local variable of method initialize instead of the instance variable.
>> So far it's clear.
>> Now, they propose a solution: to use self.one instead of just one.
>> Won't be using @one simpler and also correct ? What am I missing ?
>>
>> Thanks
>>
> 
> @one = 1 is setting the instance variable itself, and that's fine for 
> accessors. If you want to do something special on =() then you will want 
> to use the self.one style. e.g.
> 
> def Foo
>   def one=(n)
>     @one = n+42
>   end
>   def initialize(n)
>     self.one = 0 # @one == 42
>     @one = 0     # @one == 0
>   end
> end

I really wish Ruby required explicit locals declaration.  There are many 
advantages to this, including fix of the problem above, hard to debug spelling 
mistakes, clearer code, etc.  A simple 'var' declaration would be simple:

def Foo
   def one=(n)
     @one = n+42
   end
   def initialize(n)
     var x, y = n * n, 1 / n
     one = 0      # @one == 42
     @one = 0     # @one == 0
     z = 10       # error
   end
end


Regards,
Mike