From: ghorner <gabriel.horner@...>
Date: 2009-05-22T13:27:18+09:00
Subject: what's the purpose of IRB.conf[:CONTEXT_MODE] and/or 	TOPLEVEL_BINDING?

Hi all,
  I'm peering into irb's internals and am wondering what's the purpose
of IRB.conf[:CONTEXT_MODE]? I understand most of the ruby code but all
my googling has yet to bring up _anyone_ who uses this. Here is a link
to the beginning of it's implementation in irb:
http://github.com/akitaonrails/ruby191-stable-mirror/blob/c1a8d6cd2bd595ae3985edd2314f48d3d1a92188/lib/irb/workspace.rb#L21

To summarize the implementation, IRB.conf[:CONTEXT_MODE] can be set to
one of 4 values: 0,1,2,3 (default is 3). Depending on the value, a
binding is created for use when evaluating a line in irb:

0: eval("proc{binding}.call", TOPLEVEL_BINDING ...)
1: creates a binding to a temporary file
2: thread friendly binding from an irb file
3: eval("def irb_binding; binding; end; irb_binding",
TOPLEVEL_BINDING ...)

Right off the bat, I don't know the use cases for cases 1 and 2. Is a
binding in a temporary file perhaps more secure? As for cases 0 and 3
rue on irc helped me understand the difference between them: case 0
the binding has access to local variables of TOPLEVEL_BINDING while
case 3 doesn't. But when I grep in ruby's source, the only mention of
TOPLEVEL_BINDING is in irb libs and erb.rb. So of what use is case 0
when almost no libraries use TOPLEVEL_BINDING and when the binding
could just very well be TOPLEVEL_BINDING itself?

Thoughts, insights?
Thanks,
Gabriel