Protected methods: not clear to me and highly confusing

Rails
1

class Person

def initialize(name,age)
    @name,@age = name,age
end

def <=>(other)
    age <=> other.age
end

attr_reader :name,:age
protected :age

end

p1 = Person.new(“Fred”,21)
puts p1.age

That causes an error:
NoMethodError: protected method `age’ called for #<Person:0x2dc876c
@age=31,
@name=“fred”>
from (irb):41

However check this one out.
p2 = Person.new(“John”,23)
compage = (p1 <=> p2)

This one works.

My question is how come “other.age” works however “p1.age” doesn’t . I
guess
it has something to do with scope. Can someone put the explanation in an
easy to understand
sentence.

2

That’s how ruby works.
http://weblog.jamisbuck.org/2007/2/23/method-visibility-in-ruby

This is a ruby-talk question :slight_smile:

On 8/6/07, Neeraj K. [email protected] wrote:

attr_reader :name,:age

sentence.

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Cheers!

3

First off you are giving Ruby some confused signals.

attr_reader says to creat public accesor age. Then you declare age as
protected. Protected methods are not to be accessed outside the class.
Do not define age method protected.

4

Thanks Pratik but Jamis article didn’t elaborate much. At least not for
me.

  • Neeraj
5

Hi –

On Mon, 6 Aug 2007, Neeraj K. wrote:

attr_reader :name,:age

However check this one out.
p2 = Person.new(“John”,23)
compage = (p1 <=> p2)

This one works.

My question is how come “other.age” works however “p1.age” doesn’t . I guess
it has something to do with scope. Can someone put the explanation in an
easy to understand sentence.

At the time you call a protected method on x, self must be an instance
of the same class (or a subclass) as x.

That is true inside <=>, where both self and other are of class
Person. But it’s not true at the top level, where p1 is a Person but
self is the Object instance main (the top-level default object).

You should, as another poster suggested, have a look at the ruby-talk
list if you have Ruby-specific questions – not because they’re not
directly relevant to Rails development but because they’ll fit in
better there and probably get more response overall.

David

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