From: Hans Fugal <fugalh@...>
Date: 2006-03-12T13:08:46+09:00
Subject: Re: attribute setters for instance variables

Mike Austin wrote:
> 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:

What problem? I don't see any problem, I quite like that behavior. I 
also like not declaring variables, the inconvenience from spelling 
errors is minimal, especially when the telltale nil problems are almost 
as useful as a compiler error most of the time.