Issue #6710 has been reported by ko1 (Koichi Sasada).

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Feature #6710: new special binding specifier :isolated
https://bugs.ruby-lang.org/issues/6710

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


=begin

= Abstract

New special binding specifier :isolated for the 2nd argument of eval() method.
eval(src, :isolated) evaluates `src' program on the same environment as `require' and 'load'.
It is a bit different from `TOPLEVEL_BINDING'.

= Background

We have TOPLEVEL_BINDING to evaluate source code on the main environment (self is `main', and so on).
However, TOPLEVEL_BINDING contains local variables which are evaluated in toplevel.

For example:

  x = 10
  eval('a=1', TOPLEVEL_BINDING)
  eval('b=2', TOPLEVEL_BINDING)
  eval('c=3', TOPLEVEL_BINDING)
  eval('p (a+b+c) * x', TOPLEVEL_BINDING) #=> 60

To simulate "require()" or "load()" method, the eval() method with TOPLEVEL_BINDING is not enough (require() and load() methods don't evaluate scripts within `main' environment.  Similar to `main' environment (self == main), but local variables aren't take over).

BTW, eval() receive special binding specifier `nil' (which means current binding).

= Proposal

Introduce the new special binding specifier :isolated for the 2nd argument of eval() method.

eval(src, :isolated) evaluates `src' program on the new binding, which is same environment as `require' and 'load'.


== Usecase

Users can define toplevel methods, modules, classes on the any places.

  def m
    # define toplevel method foo()
    eval('def foo(); end', :isolated)
  
    # define ::Bar class
    eval('class Bar; end', :isolated)
  end

Users can make your own alternative require() method.

  def my_require(feature)
    ... # set src from feature
    eval(src, :isolated)
    ...
  end

== Consideration

* :isolated is good name or not?

I'm not sure the `isolated' is good name or not.

* ISOLATED_BINDING = :isolated

If make default constants ::ISOLATED_BINDING as a :isolated, then we can use it as `eval(src, ISOLATED_BINDING)', similar manner with TOPLEVEL_BINDING.

= Acknowledgment

Usa-san proposed the name `isolated'.  My first idea of this name is `empty'.

=end



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