From: webber han <lists@...>
Date: 2012-10-26T04:29:29+09:00
Subject: Re: Name/symbol/object type clash? What is happening here?

Todd B. wrote in post #1080823:
> It's nonsense code, but I'm curious as to what is going on behind the
> scenes...
>
> irb(main):001:0> S = Struct.new(:num)
> => S
> irb(main):002:0> class S; def change_to n; @num = n; end; end
> => nil
> irb(main):003:0> s = S.new(3)
> #<struct S num=3>
> irb(main):004:0> s.num = 4
> => 4
> irb(main):005:0> s.num
> => 4
> irb(main):006:0> s.change_to(5)
> => 5
> irb(main):007:0> s.num
> => 4
> irb(main):008:0> s.instance_variables
> => [:@num]
> irb(main):009:0> s.instance_variable_set(:@num, 5)
> => 5
> irb(main):010:0> s.num
> => 4
>
> Same thing happens if I don't define class S, but just define a method
> on the instance... def s.change_to n; @num = n; end

Ruby is not screwed up!

Think about why do you want to use Struct at first place, what Struct
gives you? If you think in this direction, then it makes sense that
those attribute created when you instantiate a Struct are encapsulated.
It is the responsibility of the Struct to handle those data not the
class you created using something like Foo = Struct.new. If you really
need a instance variable with the same name as one of the attribute from
Struct, why on earth would you need Struct at the beginning?

High-levelly speaking, Struct gives you something as simple as
Hash(since you can do things like obj['attr'] when obj is a struct, and
you can iterate!), but less than a real class (you are not able to
define a method on struct).

The idea is, Struct is awesome if you don't need the power of Class, but
you want to bring more domain into your code not just a hash like data
structure.

Remember, Ruby is awesome and will be awesome forever! Just kidding, it
won't...

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