Problem with method

ruby-talk
1

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

···

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2

I'm not entirely sure what you're trying to do. Does this accomplish
what you want?

    class Kolo
      include Domieszka

      def pole=(r)
        @r = r
        r * Math::PI
      end
    end

Note that PI is a constant within Math's namespace, and not a method.
The period is used as a method call operator; the double-colon is a
namespace separator, used to access constants within the module's
namespace.

Also note that the pole= definition needs to have an argument defined for
it if you want to use that argument -- which I think is what you were
trying to do with that "r".

···

On Fri, Feb 03, 2012 at 11:55:13AM +0900, luk malcik 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

--
Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]

3

I mean that Pole= is the same as Pole_is. I want to declare accessors to
write pole and read pole: pole= and pole. Of course Math::PI * r**
// my mistake

···

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4

pole= is the name of the method

···

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5

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.

···

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

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