[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

const_defined? not quite in sync with const_get ??

chrisjroos@gmail.com

9/20/2006 5:07:00 PM

Assuming the following snippet, I'd expect Foo::const_defined?(:Bar)
to be routed via Foo::const_missing. Instead it resolves to top-level
Bar. Can someone explain why please?

--code--

class Bar
end

module Foo
def self.const_missing(konst)
puts "missing konst #{konst}"
end
end

Foo::Bar
#=> missing konst Bar # Unsurprising behaviour

p Foo::const_defined?(:Bar)
false # Unsurprising behaviour

p Foo::const_get(:Bar)
#=> Bar # Surprising behaviour

--/code--

Cheers,

Chris
6 Answers

Ara.T.Howard

9/20/2006 5:19:00 PM

0

chrisjroos@gmail.com

9/20/2006 5:35:00 PM

0

> non-prefixed constants follow the normal scoping rules:
>
Thanks for the clarification. Purely out of interest, do you find
this behaviour a bit odd (or am I missing obvious reasons as to why it
is implemented this way)?

Chris

Ara.T.Howard

9/20/2006 5:58:00 PM

0

chrisjroos@gmail.com

9/20/2006 8:24:00 PM

0

>
> so that
>
>
> class C
> a = Array.new # up scope
> end
>
>
> and
>
> class C
> a = const_get('Array').new
> end
>
> behave
>
> i agree it can be confusing, but the alternative, requiring all constants to
> be fully scoped, would be an enormous pain in the ass.
>
Ah, of course, that makes sense. Cheers.

Nobuyoshi Nakada

9/21/2006 3:40:00 AM

0

Date: Thu, 21 Sep 2006 02:06:56 +0900
Posted: Wed, 20 Sep 2006 18:06:54 +0100
From: "Chris Roos" <chrisjroos@gmail.com>
Reply-To: ruby-talk@ruby-lang.org
Subject: const_defined? not quite in sync with const_get ??
To: ruby-talk@ruby-lang.org (ruby-talk ML)
Message-Id: <3a5e51050609201006j5dc6449cyae74e71099fb3f52@mail.gmail.com>
X-ML-Name: ruby-talk
X-Mail-Count: 215393


2006/9/21, Chris Roos <chrisjroos@gmail.com>:
> Assuming the following snippet, I'd expect Foo::const_defined?(:Bar)
> to be routed via Foo::const_missing. Instead it resolves to top-level
> Bar. Can someone explain why please?
>
> --code--
>
> class Bar
> end
>
> module Foo
> def self.const_missing(konst)
> puts "missing konst #{konst}"
> end
> end
>
> Foo::Bar
> #=> missing konst Bar # Unsurprising behaviour
>
> p Foo::const_defined?(:Bar)
> false # Unsurprising behaviour
>
> p Foo::const_get(:Bar)
> #=> Bar # Surprising behaviour
>
> --/code--
>
> Cheers,
>
> Chris
>
>


--
??????

--
--- ????Bug????
--- ?????Bug?????
?? ??

Nobuyoshi Nakada

9/21/2006 3:42:00 AM

0

Hi,

Sorry for mispost.

At Thu, 21 Sep 2006 02:06:56 +0900,
Chris Roos wrote in [ruby-talk:215393]:
> Foo::Bar
> #=> missing konst Bar # Unsurprising behaviour
>
> p Foo::const_defined?(:Bar)
> false # Unsurprising behaviour
>
> p Foo::const_get(:Bar)
> #=> Bar # Surprising behaviour

It has changed in 1.9.

p Foo::const_defined?(:Bar) #=> true

p Foo::const_get(:Bar) #=> Bar

p Foo::const_defined?(:Bar, false) #=> false

p Foo::const_get(:Bar, false) #=> missing konst Bar

--
Nobu Nakada