From: Robert Klemme <shortcutter@...>
Date: 2010-01-27T00:07:48+09:00
Subject: Re: Why is the Binding object so useless?

2010/1/25 Tony Arcieri <tony@medioh.com>:
> I am used to Ruby being a rather reflective language that gives carte
> blanche to the programmer.  So I found this rather surprising:
>
>>> Marshal.dump binding
> TypeError: no marshal_dump is defined for class Binding
>
> Whaa?

I don't think it does make sense to serialize a binding for the same
reason that you cannot create a new binding: a binding is bound to a
particular program context - I assume this also includes caller stack
and other internal state.

Even if a binding contains local variables what is the effect of
deserializing a binding?  If your local variables get updated that is
certainly not a good idea.  If you want to serialize state use objects
with the proper state.

>>> Binding.new
> NoMethodError: undefined method `new' for Binding:Class
>
> Huh?

A binding is not a regular object but it is a handle on the state of
the runtime.  A method object cannot be serialized as well because
that would mean that the original code would have to be written (and
read); this also has security implications (in the case of Method).

But if you have to_hash you can serialize that.

> I would expect you to be able to do all of the above.  In addition to that,
> it's sure be nice to do some of the following:
>
>>> Binding.new :a => 1, :b => 2, :c =>3
> => #<Binding:0x1018130b0> # new binding object with the given variables
> bound

As above.

>>> binding.to_hash
> => {:a => 1, :b => 2, :c => 3} # Bound variables, as a hash
>>> binding.to_yaml
> => "--- !ruby/object:Binding \na: 1\nb: 2\nc: 3\n" # YAML dump of a Binding
> object

Same as above for Marshal.

> And hey, maybe Binding#inspect could give a little more information than its
> object_id?

Yeah, #to_hash and #inspect sound pretty good.  You might even add a
method #update receiving a Hash which is interpreted as a mapping from
local variables to values and which overwrites the current binding.

Kind regards

robert

-- 
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