From: Daniel Bye <ruby@...>
Date: 2011-11-23T23:12:21+09:00
Subject: Re: private and protected

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On Wed, Nov 23, 2011 at 10:20:54PM +0900, =D0=9D=D0=B8=D0=BA=D0=BE=D0=BB=D0=
=B0=D0=B9 wrote:
> Could anybody explain me this, please?
>=20
> class First
>     def say
>         self.phrase
>     end
>=20
>     private
>=20
>     def phrase
>         'something'
>     end
> end
>=20
> a =3D First.new
> a.say
> # got
> NoMethodError: private method `b' called for #<A:0xb7756518>
>     from (irb):44:in `say'
>     from (irb):52
>     from :0
>=20
> If i write the same code with 'protected' instead of 'private' I got no=
=20
> error.
> If i write the same code with calling 'phrase' instead of 'self.phrase'=
=20
> in 'say' method I got no error again.

A private method may only be called with an implicit receiver - in
self.phrase, self is explicit, which is why you get the exception. The
practical upshot of this is that private methods may only be called by the
current instance, because the implicit receiver is understood to be "self".

Protected methods may be called by the current instance, instances of its
class or instances of it subclasses, and require an explicit receiver,
except when the receiver is the current instance. I would tend, even then,
to pass it explicitly to help make the code's intent clearer.

This has been expressed much more elegantly in numerous places, so search
the web if I only served to confuse!

Dan

--=20
Daniel Bye
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