How to implement class constants?

ruby-talk
1

hi list,

what construct do I have to use in Ruby to create class constants (so
no instance necessary to use it)?

thanks, Ruud

2

ruud wrote:

hi list,

what construct do I have to use in Ruby to create class constants (so
no instance necessary to use it)?

thanks, Ruud

This seems to work:

class Dog
  Color = 'brown'

  def Dog.Color
    Color
  end

end

puts Dog.Color

···

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3

This seems to work:

Or maybe:

class Dog
  Color = 'brown'
end

puts Dog::Color

Dog::Attrib = 'cute'

puts Dog::Attrib

4

Thank you both for you answer. I like the Class::var solution best;
the other one includes more typing.

I am fairly new to Ruby so all the time I am occupied asking myself
easy-to-answer questions. This really helps.

Another easy to answer question is a bit related:
Most of the time I find a class.var notation of a class::var notation.
In documentation I find class#method notation. How are these three
related to each other?

thanks, Ruud

5

ruud wrote:

Most of the time I find a class.var notation of a class::var notation.

That's not entirely accurate. There is no class.var. There's object.method
(where object can be a class and the method can have the same name as a
variable, but it still has to be a method) and there's namespace::Constant
where namespace can be a class or a module and Constant has to be a constant
(it can't be any other sort of variable).
The :: is for accessing constants in a namespace and the . is for calling
methods on an object.
It is not possible to access non-constant variables from outside the class
without using methods designed for that purpose.

In documentation I find class#method notation. How are these three
related to each other?

class#method describes an instance method (as opposed to class.method which
would describe a class method). If you see something like String#length, that
means that you could e.g. write "hello".length, but not String.length. If you
see String.new, you have to actually type String.new and not something
like "hello".new.

HTH,
Sebastian

···

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6

Sebastian,
it couldn't have been clearer. Thank you for your extensive reply!

Ruud

···

On 18/02/2008, Sebastian Hungerecker <sepp2k@googlemail.com> wrote: