Problem with method

Ruby
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

2

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

  @x = x

end
end

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”.

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

4

pole= is the name of the method

5

On Thu, Feb 2, 2012 at 8:55 PM, luk malcik [email protected] wrote:

module 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.