From: Raul Parolari <raulparolari@...>
Date: 2007-11-12T14:30:46+09:00
Subject: Re: Controlling attribute setting in a Struct

unknown wrote:
> I'm using a bunch of Struct classes in a program; they're a perfect
> way for me to bundle and access attributes. But in one of my
> subclasses of Struct, I'm trying to control setting attributes so that
> setting an attribute above a certain value causes an effect
> ...

You just need to redefine the setter attribute; we can automate the 
production of the setter attributes as follows (I assume that the 
maximum has the same value for all attributes, else this would need to 
be modified a bit):


class MyMaxBoundedStruct < Struct.new(:life, :strength, :charisma, 
:weapon)

  # class variable (depending on Spec, a Constant could be used)
  @@maximum = 1000

  arr = %w[life strength charisma weapon]

  arr.each do |m|
    define_method("#{m}=") do |val|
      if val < @@maximum
        super(val)
      else
        raise ArgumentError, "#{m} set above maximum"
      end
    end
  end

end

rabbit = MyMaxBoundedStruct.new

rabbit.life   = 999
rabbit.weapon = 10
p rabbit.life       # => 999

rabbit.life = 1000  # => ArgumentError: life set above maximum
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