[ruby-core:56471] [ruby-trunk - Feature #8761][Open] Binding#local_variable_get, set, defined?

Issue #8761 has been reported by ko1 (Koichi Sasada).

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Feature #8761: Binding#local_variable_get, set, defined?
https://bugs.ruby-lang.org/issues/8761

Author: ko1 (Koichi Sasada)
Status: Open
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: 
Target version: 


I propose new 3 methods of Binding.

- Binding#local_variable_get(sym)
- Binding#local_variable_set(sym)
- Binding#local_variable_defined?(sym)

Maybe you can imagine the behavior.

These methods help the following cases:

(1) Access to special keyword arguments

From Ruby 2.0, we can use keyword arguments. And further more, you can use special keyword named such as `if', `begin' and `end', the language keyword.

However, of course you can't access the local variable `if', because of syntax error.

For example,

  def access begin: 0, end: 100
    p(begin) #=> syntax error
    p(end)   #=> syntax error
  end

To access such a special keyword parameter, you can use Binding#local_variable_get(sym)

  def access begin: 0, end: 100
    p(binding.local_variable_get(:begin)) #=> syntax error
    p(binding.local_variable_get(:end))   #=> syntax error
  end

(2) Create a binding with specific local variables

If you wan to make a binding which contains several local variables, you can use Binding#local_variable_set to do it.
(See [Feature #8643])


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Implementation note:
I think Binding is good place to put these methods than Kernel.
Using binding make it clear that it is need to access to a local environment.
It will help optimization (don't interrupt optimization).

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You can try these methods on ruby 2.1dev (trunk), committed at r42464.
Your comments are welcome.

This proposal was discussed at dev-meeting at Japan 
https://bugs.ruby-lang.org/projects/ruby/wiki/DevelopersMeeting20130727Japan
and Matz accepted it.



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