Surprising behavior when extending instances

[Jim Crossley]

This surprised me:

module English; def say; "yes"; end; end
module French; def say; "oui"; end; end
x = Object.new
x.extend English
x.say # "yes"
x.extend French
x.say # "oui"
x.extend English
x.say # "oui"

What wrong assumptions am I making that this surprises me? What is
the more elegant "Ruby way" of alternating an object's behavior at
runtime?

Thanks,
Jim

 

[Rick DeNatale]

This surprised me:

=A0module English; def say; "yes"; end; end
=A0module French; def say; "oui"; end; end
=A0x =3D Object.new
=A0x.extend English
=A0x.say =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 # "yes"
=A0x.extend French
=A0x.say =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 # "oui"
=A0x.extend English
=A0x.say =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 # "oui"

What wrong assumptions am I making that this surprises me?

Matz has already explained that module inclusion is a one-time only deal.

Here's a bit on why that is.

http://talklikeaduck.denhaven2.com/2007/11/03/a-chat-with-matz-classs-varia=
ble-reversion-and-a-mystery-explained

=A0What is
the more elegant "Ruby way" of alternating an object's behavior at
runtime?

I'd use a form of delegation

module English; def self.agree; "yes"; end; end
module French; def self.agree; "oui"; end; end

class Speaker

attr_accessor :language

def initialize(language =3D English)
self.language =3D language
end

def say
language.agree
end

def speak(language)
self.language =3D language
end
end

jack =3D Speaker.new
jacques =3D Speaker.new(French)

jack.say # =3D> "yes"
jacques.say # =3D> "oui"

jack.speak(French)
jacques.speak(English)

jack.say # =3D> "oui"
jacques.say # =3D> "yes"

jack.speak(English)
jacques.speak(French)

jack.say # =3D> "yes"
jacques.say # =3D> "oui"





--=20
Rick DeNatale

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