From: Josh Cheek <josh.cheek@...>
Date: 2012-02-03T13:00:46+09:00
Subject: Re: problem with method

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On Thu, Feb 2, 2012 at 8:55 PM, luk malcik <aport99@gmail.com> wrote:

> Why method pole= doesn't work??
>
>
>
>
>
> Kolo = Struct.new (:x,:y,:r)
> Kwadrat = Struct.new (:x,:y,:a)
> Prostokat = Struct.new (:x,:y,:a,:b)
>
> module Domieszka
>   attr_accessor :x, :y
>
>   def moveto(x,y)
>      @x = x
>      @y = y
>   end
> end
>
> class Kolo
>   include Domieszka
>   def pole=
>   @r = r
>   pole = r * Math.PI
>   return pole
>   end
> end
>
> --
> Posted via http://www.ruby-forum.com/.
>
>
There's a bunch of things here to pay attention to.

* Methods ending in equal signs need paramaters. e.g. `def pole=(radius)`

* Assignments in Ruby always return the RHS of the assignment, so your
explicit `return pole` won't work.

* If you want the parentheses to delimit a method call, you must put them
directly after the name (to avoid ambiguous syntax). So this means
`Struct.new(:a, :b, :c)` not `Struct.new (:a, :b, :c)`

* Structs don't store their data in instance variables of the given name,
so when you say `@r = r` you're not setting the variable that will be
returned when the method r is invoked. Instead, use the setter that the
struct provides (I consider this the right way to set things, anyway) So
`self.r = r`

* There are some other options for your Kolo class that I think wold be
better:

Kolo = Struct.new :x, :y, :r do
  def pole=(...)
    ...
  end
end

or alternatively

class Kolo < Struct.new(:x, :y, :z)
  def pole=(...)
    ...
  end
end

I like both of these better than reopening the class later.

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