C extensions and class constants nested within modules

[Daniel Berger]

Hi all,

This appears to be perfectly legal Ruby code:

module Foo
class Bar
end
class Bar::Baz
end
end

p Foo::Bar.new # ok
p Foo::Bar::Baz.new # ok

However, an equivalent C extension has problems:

void Init_foo(){
VALUE mFoo = rb_define_module("Foo");
VALUE cBar = rb_define_class_under(mFoo, "Bar", rb_cObject);
VALUE cBarBaz = rb_define_class_under(mFoo, "Bar::Baz", rb_cObject);
}

p Foo::Bar.new # ok
p Foo::Bar::Baz.new # uninitialized constant Foo::Bar::Baz (NameError)

Why doesn't that work?

The only way I could get it to work was to declare "Baz" under "Bar". But is
that really the same thing?

Regards,

Dan

PS - I may have asked this before, but I'm old, my mind is going and Google is
failing me.

 

[ts]

D> Why doesn't that work?

Because this is parse.y and eval.c which make work

class Bar::Baz
end

and not the call to rb_define_class()

With rb_define_class("Bar::Baz"), ruby has defined a class "Bar::Baz" and
not a class Baz under Bar (what it look with Foo::Bar::Baz)

D> The only way I could get it to work was to declare "Baz" under "Bar". But is
D> that really the same thing?

In your case probably.


Guy Decoux

 

[Daniel Berger]

D> Why doesn't that work?

Because this is parse.y and eval.c which make work

class Bar::Baz
end

and not the call to rb_define_class()

With rb_define_class("Bar::Baz"), ruby has defined a class "Bar::Baz" and
not a class Baz under Bar (what it look with Foo::Bar::Baz)

D> The only way I could get it to work was to declare "Baz" under "Bar". But is
D> that really the same thing?

In your case probably.

What's the difference between these two?

module Foo
class Bar
end
class Bar::Baz
end
end

module Foo
class Bar
class Baz
end
end
end

Is there any difference? What are the potential pitfalls, if any?

Thanks,

Dan

 

[Mauricio Fernández]

What's the difference between these two?

module Foo
A = :Foo
class Bar
A = :Bar
end
class Bar::Baz
A # => :Foo
end
end

module Foo
class Bar
class Baz
A # => :Bar
end
end
end

RUBY_VERSION # => "1.8.3"