Modules

Ruby
1

I understand the way these things are working but I don’t really
understand what’s going on and why.

module Foo
def bar
1
end
def Foo.zim
2
end
end

Foo.zim # works, OK, fair enough
2

Foo::zim # works, but why have two syntaxes that do the same?
2

Foo.bar # NoMethodError. Shouldn’t this work though? What if I had a procedural API that I wanted to namespace: -

module SomeNamespace
require ‘procedural_api’
end

SomeNamespace.function_from_procedural_api # this ain’t gonna work!
SomeNamespace::function_from_procedural_api # nor is this

class SomeClass
include Foo
end

SomeClass.new.bar # OK, it’s been mixed in
1

SomeClass.zim # NoMethodError, huh? Why doesn’t this work?
SomeClass.new.zim # NoMethodError. So where has the zim definition actually gone? Doesn’t it get included at all?

I’m very confused by all this. Please help unravel the mess in my brain.

2

Oliver S. [email protected] wrote:

end
end

SomeClass.new.bar # OK, it’s been mixed in
1
SomeClass.zim # NoMethodError, huh? Why doesn’t this work?
SomeClass.new.zim # NoMethodError.

I’m very confused by all this. Please help unravel the mess in my brain.

I’d say you’re not confused at all. You’ve described perfectly how the
language behaves.

m.

3

Foo.zim # works, OK, fair enough
2

Foo::zim # works, but why have two syntaxes that do the same?
2

objec.method works for any object. Everything is an object, so Foo is
an object too.
Class::method, Module::method works with class/module methods only.

SomeClass.zim # NoMethodError, huh? Why doesn’t this work?
SomeClass.new.zim # NoMethodError.

Let’s take a different angle:

class Baz
def Baz.qux # class method. you can look at it as a singleton method for Baz
3
end
end
=> nil

Baz.qux
=> 3

Baz.new.qux # class method is not available to the instance
NoMethodError: undefined method `qux’ for #Baz:0x35c6f4
from (irb):7
from :0

Thus zim exists only for the object of the Foo module - not any class
that mixes in Foo, just for THE Foo itself.

Regards,
Rimantas