Question about self and private

Rails
1

Hi!

There’s something I don’t understand yet about static/private methods. I
hope someone can explain…

E.g.:

class SayHello
def hello(who)
puts "Hello, " + who + “!”
end
def self.say(words)
puts words
end
end

hello = SayHello.new
hello.hello “World” : Hello World!
hello.say “hi” : Error
SayHello.say “hi” : hi

OK, this is clear to me, but now…

class SayHello
private
def hello(who)
puts "Hello, " + who + “!”
end
def self.say(words)
puts words
end
end

Both methods are private now.

hello = SayHello.new
hello.hello “World” : Error because the method is private
hello.say “hi” : Error because the method is static
SayHello.say “hi” : hi

The last one I don’t understand. How come it returns “hi” eventhough
it’s a private method? Can someone shed some light?

Thanks,
Mischa.

2

Mischa B. wrote:

Both methods are private now.
Nope private, protected and public modifiers have only effect on
instance
methods (that have an implicit “self” as receiver). If you want to
define
a private class method you need to make available that implicit “self”:

class SayHello
private
def hello(who)
puts "Hello, " + who + “!”
end
class << self
private
def say(words)
puts words
end
end
end

Now both methods are private. You can only call them on self, this means
that SayHello.say is only callable by another class method.

zsombor

3

On Tue, 2006-01-17 at 11:29 +0200, Dee Z. wrote:

end
end

You can’t do this though:

class SayHello
self.private
def self.say(words)
puts words
end
end

as “private” is itself a private method :slight_smile:

NoMethodError: private method `private’ called for SayHello:Class

4

Dee Z. wrote:

end

Both methods are private now.

Nope private, protected and public modifiers have only effect on instance
methods (that have an implicit “self” as receiver). If you want to define
a private class method you need to make available that implicit “self”:

Well, actually I was asking cause I saw a code sample in the “Agile Web
Development with Rails” book (pp. 510: private def self.hash_password)
that didn’t make sense to me. I don’t mind my methods not being private,
so I guess I’ll just leave out “private”. Thanks for clearing things up.

Mischa.

5

class SayHello
private
def hello(who)
puts "Hello, " + who + “!”
end
def self.say(words)
puts words
end
end

An even simpler way is to use ‘private_class_method’

class SayHello
def self.say(words)
puts words
end
private_class_method :say
end

Zsombor