From: Josh Cheek <josh.cheek@...>
Date: 2011-01-26T04:06:24+09:00
Subject: Re: General Ruby Object Oriented

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On Tue, Jan 25, 2011 at 12:33 PM, Jim Carter <jcarter@leupold.com> wrote:

>
> def initialize(&block)
> instance eval &block
> end
>
>
This should be instance_eval (with an underscore)


> tc = BasicMath.new
> puts tc.add(a,b,c)
> puts tc.calc_nrows(5.0,3.0,1.0)
>
>
This code is inside your class definition. So, at that time, self is that
class, not an instance of that class. How about wrapping it in a method
called calculate, so that its instances can call that code by invoking the
calculate method:
  def calculate
    tc = BasicMath.new
    puts tc.add(a,b,c)
    puts tc.calc_nrows(5.0,3.0,1.0)
  end

desktop = ExternalBallistics.new do
> self.a = 5.0
> self.b = 3.0
> self.c = 1.0
> end
>

Then we would just need to stick a call to calculate in the block:

desktop = ExternalBallistics.new do
  self.a = 5.0
  self.b = 3.0
  self.c = 1.0
  calculate
end


On Tue, Jan 25, 2011 at 12:54 PM, Jim Carter <jcarter@leupold.com> wrote:

>
> but I don't understand the authors assignment of self.a, self.b, self.c,
> especially in light of the fact that it doesn't work.  If anyone can
> share any insight, I'd appreciate it.
>
>
In ExternalBallistics#initialize, you instance_eval the block. That sets
self to be the instance that is created when you do ExternalBallistics.new,
so when you are in the block and say self.a=5.0, you are telling it to
invoke the method a= and pass it the value 5.0

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