a little challenge - reproduce this error

[Intransition]

Want to see a really amazing error I got this week? Okay... but to
make it more interesting I am going to the change some names to
protect the innocent, and offer up a little challenge: How can
reproduce it?

The error is this:

uninitialized constant X::Foo::X (NameError)

Did you catch that?

Think you can solve it?

I imagine your mind is getting a bit mushy about now ;-)

 

[Steve Klabnik]

[Note: parts of this message were removed to make it a legal post.]

throw NameError.new("uninitialized constant X::Foo::X")

 

[John Feminella]

This is a pretty trivial error to generate. Just reference the
constant that doesn't exist:

$ irb
ruby-1.9.2-p180 :001 > module X; module Foo; end; end
=> nil
ruby-1.9.2-p180 :002 > X::Foo::X
NameError: uninitialized constant X::Foo::X

~ jf

 

[Intransition]

This is a pretty trivial error to generate. Just reference the
constant that doesn't exist:

$ irb
ruby-1.9.2-p180 :001 > module X; module Foo; end; end
=A0=3D> nil
ruby-1.9.2-p180 :002 > X::Foo::X
NameError: uninitialized constant X::Foo::X

Ah good point. I made an assumption. A qualifier then: X does exist.
How about this must be as top of your solution.

module X; end

 

[Intransition]

throw NameError.new("uninitialized constant X::Foo::X")

Oh you are a clever one ;-)

 

[Christopher Dicely]

Ah good point. I made an assumption. A qualifier then: X does exist.
How about this must be as top of your solution.

=C2=A0 =C2=A0module X; end

The top-level X (and the Foo underneath it) seems required to get the
error, so that doesn't make it harder. If you reference X::Foo::X
without X existing, you'll get
uninitialized constant Object::X (NameError)

If you reference X::Foo::X with just the part you have above, you'll
get uninitialized constant X::Foo (NameError)

The easiest way to get the error you ask about is
module X; module Foo; end; end
X::Foo::X

But I would guess that that probably isn't what you are looking for either.

 

[Christopher Dicely]

throw NameError.new("uninitialized constant X::Foo::X")

Doesn't give the right result. You want raise, not throw.

 

[Michael Edgar]

The easiest way to get the error you ask about is
module X; module Foo; end; end
X::Foo::X
=20
But I would guess that that probably isn't what you are looking for =

either.

It wouldn't be, because that's not an error: it ends up referencing the =
top-level X from inside Foo, giving this warning:

(irb):1407: warning: toplevel constant X referenced by X::Foo::X

Michael Edgar
(e-mail address removed)
http://carboni.ca/

 

[Intransition]

The top-level X (and the Foo underneath it) seems required to get the
error, so that doesn't make it harder. If you reference X::Foo::X
without X existing, you'll get
uninitialized constant Object::X (NameError)

If you reference X::Foo::X with just the part you have above, you'll
get uninitialized constant X::Foo (NameError)

The easiest way to get the error you ask about is
module X; module Foo; end; end
X::Foo::X

Well, Balls. That in itself seems ridiculous, but you are right. I'm
not sure why it raises that though. Maybe the code is silly, but is it
really wrong? Try X::Foo.const_getX) and it works fine. Seems
inconsistent, doesn't it?

But I would guess that that probably isn't what you are looking for eithe=

r.

Yes, in the actual code X is being referenced from within Foo but is
not fully qualified.

 

[Intransition]

her.

It wouldn't be, because that's not an error: it ends up referencing the t=

op-level X from inside Foo, giving this warning:

(irb):1407: warning: toplevel constant X referenced by X::Foo::X

Interesting. What platform on you on?

 

[Intransition]

Interesting. What platform on you on?

s/on/are/

I've always been pretty bad with the typos, but I swear this week I've
gone into dyslexic overdrive. My apologies.

 

[Michael Edgar]

=20
=20

=20
Interesting. What platform on you on?
=20

That was on 1.9.2p188. Seems to be a change in 1.9 - I started checking =
against other RVM installs
after seeing your response that X::Foo::X gives an error. I could've =
sworn I understood the differences
in constant resolution between 1.9.2 and 1.8.7... back to the drawing =
board there, I guess.

In fact, I can't even produce that error in 1.9.2.

Michael Edgar
(e-mail address removed)
http://carboni.ca/

 

[Michael Edgar]

=20
That was on 1.9.2p188. Seems to be a change in 1.9 - I started = checking
against other RVM installs after seeing your response that X::Foo::X
gives an error. I could've sworn I understood the differences in
constant resolution between 1.9.2 and 1.8.7... back to the drawing
board there, I guess.
=20
In fact, I can't even produce that error in 1.9.2.

=20
It works the same both 1.8.7, 1.9.1, and 1.9.2 for me.
=20
--=20
Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]

... and my contribution becomes meaningless. Ugh. I closed my irb =
session and re-opened
it, and now can't repro the top-level dereference. If I can, I'll post, =
but I'm guessing I should
have just used a fresh session instead one that appears to have been =
1500 evaluations deep.

Sorry for the confusion/noise,

Michael Edgar
(e-mail address removed)
http://carboni.ca/

 

[Christopher Dicely]

It wouldn't be, because that's not an error: it ends up referencing the top-level X from inside Foo, giving this warning:

(irb):1407: warning: toplevel constant X referenced by X::Foo::X

Michael Edgar
(e-mail address removed)
http://carboni.ca/

 

[Christopher Dicely]

Well, Balls. That in itself seems ridiculous, but you are right. I'm
not sure why it raises that though. Maybe the code is silly, but is it
really wrong? Try X::Foo.const_getX) and it works fine. Seems
inconsistent, doesn't it?

Not really. I'd expect X::Foo::X to get the constant at that path
(which doesn't exist, hence the error), while X::Foo.const_getX) I'd
expect to resolve as if X was referenced within X::Foo, including
climbing up the chain, and to return the top-level X.

Yes, in the actual code X is being referenced from within Foo but is
not fully qualified.

I could swear that I have run into that error in some things in the
past (and resolved it by fully qualifying the affected references),
but now I can't figure out how to reproduce it.

 

[Intransition]

I could swear that I have run into that error in some things in the
past (and resolved it by fully qualifying the affected references),
but now I can't figure out how to reproduce it.

I realize now maybe how I should have phrased this as a challenge

module X
class Foo
def call
X
end
end
end

Change one line of this code to cause this error:

uninitialized constant X::Foo::X (NameError)

and without directly calling #raise.

Something like that anyway. Hindsight being 20/20 and all. Of course,
I made it a challenge simply b/c I thought it would be a bit more
interesting that way.

I let this sit for a bit longer then I'll give the lowdown and a
useful tip on how to deal with it when it arises.

 

[John Feminella]

I realize now maybe how I should have phrased this as a challenge

=C2=A0 =C2=A0module X
=C2=A0 =C2=A0 =C2=A0class Foo
=C2=A0 =C2=A0 =C2=A0 =C2=A0def call
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0X
=C2=A0 =C2=A0 =C2=A0 =C2=A0end
=C2=A0 =C2=A0 =C2=A0end
=C2=A0 =C2=A0end

Change one line of this code to cause this error:

=C2=A0uninitialized constant X::Foo::X (NameError)

and without directly calling #raise.

Just to be clear, do you mean "without invoking #call" (as in, pasting
this into irb should raise the error), or is the intention that #call
will be invoked?

 

[Intransition]

Just to be clear, do you mean "without invoking #call" (as in, pasting
this into irb should raise the error), or is the intention that #call
will be invoked?

When #call is invoked, the error is raised. So yea, guess I should
have added:

X::Foo.new.call

 

[Josh Cheek]

[Note: parts of this message were removed to make it a legal post.]

When #call is invoked, the error is raised. So yea, guess I should
have added:

X::Foo.new.call

Well, I give up

 

[Intransition]

Well, I give up

I bet a few people have come across it without fully knowing what was
going on and just fixed their issue by adding `::` to the "X". That's
what I did a few times before I realized what the hell was going on.

The change needed to cause the error is this:

module X
class Foo < BasicObject
def call
X
end
end
end

Right off you can see this only effect Ruby 1.9+ (b/c 1.8 has no
BasicObject).

Next up... why it happens and how to fix.