From: gwtmp01@...
Date: 2007-01-19T08:07:04+09:00
Subject: Re: auto assign arguments?


On Jan 18, 2007, at 5:06 PM, Gregory Brown wrote:
> BUT... it's be okay if you could build this as a module, I think.
> Then you could just include it in a class to get the behavior when it
> is appropriate.

The code below uses instance_exec from ruby 1.9. It will still work
under ruby 1.8 as long as you don't give a block to the #init method.

Gary Wright

module Init
   def init(*syms, &iproc)
     define_method(:initialize) {|*x|
       raise ArgumentError, "wrong number of arguments: #{x.size} for  
#{syms.size}" if x.size != syms.size
       syms.zip(x).each { |sym, val|
         instance_variable_set("@#{sym}", val)
       }
       instance_exec(*x, &iproc) if iproc
     }
   end
end

class A
   extend Init
   init :a, :b, :c, :d
end

a = A.new(1,2,3,4)
p a.instance_variables			# ["@b", "@a", "@c", "@d"]
a.instance_variables.each { |n|
   puts "#{n} = #{a.instance_variable_get(n)}"
}

class Object
   extend Init
end

class B
   attr :attr1, :attr2
   init :attr1, :attr2
end

b = B.new('foo', 'bar')
p b.attr1       # 'foo'
p b.attr2       # 'bar'

class C
   init :c, :d do
     puts "@c is #{@c}"
     puts "@d is #{@d}"
   end
end

C.new(3,4)	  # @c is 3
                   # @d is 4
begin
   C.new(5)        # argument error
rescue
   p $!
end