From: Brian Candler <b.candler@...>
Date: 2010-09-23T17:17:49+09:00
Subject: Re: Unexpected behaviour of defined? under 1.8.x

Rick Denatale wrote:
>> I would expect defined? line to raise an RuntimeError,...
> 
> Why?
> 
> defined? is there to check WITHOUT raising an runtime error

I think the point is the autoload stuff.

If you have autoload set up for A::B, and you are checking "defined? 
A::B::C", then of course A::B has to be autoloaded before you check 
A::B::C. But when an exception is raised in the source file which is 
being autoloaded, it just finishes at that point silently, so you end up 
with half a file loaded.

Here is another example:

---- a.rb ----
module A
  autoload :B, "b.rb"
end

p defined?(A::B::C)   # nil
p defined?(A::B::C)   # "constant"

---- b.rb ----
module A
  class B
    puts "Starting"
    C = 123
    raise "Oops"
    puts "Never get here"
  end
end
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