From: Jim Carter <jcarter@...>
Date: 2011-01-26T03:33:26+09:00
Subject: General Ruby Object Oriented

I'm a newbie to Ruby (hmm... rhymes) and to object oriented programming
in general, so having a hard time wrapping my mind around a paradigm
which differs from C language. Here is a short snippet of code, the
general flow coming from the book "The Ruby Way" (pg 392).

The class ExternalBallistics would be the equivalent of my top level
function (or container of functions) which will get inputs from the Main
(in this case rails text and selection box fields) and will calculate a
series of results.

desktop is supposed to define those variables, which ExternalBallistics
can then apply to its various methods. However, it is not working out
that way. Ruby is complaining that the variables a, b and c are not
defined. Note that the relationship between ExternalBallistics and
BasicMath is OK, but the relationship between desktop and
ExternalBallistics is not, as if I am not using the attributes
incorrectly. Can someone help me here.


class BasicMath
# Could be called as a class, static, method

# attr_accessor :a, :b, :c

def add(a, b, c)
m = (a + b - c)/b
n = a + b
return m, n
end


def calc_nrows(a, b, c)
nrows = (a - b)/c
return nrows.round
end

end


class ExternalBallistics

attr_accessor :a,:b,:c

def initialize(&block)
instance eval &block
end

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

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