From: merch-redmine@...
Date: 2019-07-05T18:05:27+00:00
Subject: [ruby-core:93564] [Ruby master Bug#11304] [PATCH] Kernel.global_variables should observe $~.

Issue #11304 has been updated by jeremyevans0 (Jeremy Evans).


All of the other similar regexp variables (`$& $' $+ $~ $(backquote)`) are listed by `global_variables`, so it would make sense for `$1` and similar to appear, or alternatively for the other 5 regexp globals not to appear if there is no match.    If there is no backref, the other 5 regexp globals still appear.  If there is a backref, and it has no captures, it doesn't make sense for `$+` to be included and `$1` not to be included.

I'm not sure whether `$1` through `$9` should be present for consistency, even the last match did not have that number of captures.  I think that would be more consistent to include all of them if we are including `$+` in the case of no matches.  However, that would make `global_variables` less consistent with `defined?`.

Related to this, `defined?` is a little strange for the regexp globals:

```ruby
puts %w[$~ $& $` $' $+ $1 $2].map{|s| "#{s}: #{eval("defined?(#{s})").inspect}"}
# $~: "global-variable"
# $&: nil
# $`: nil
# $': nil
# $+: nil
# $1: nil
# $2: nil

/(.)/ =~ "a"
puts %w[$~ $& $` $' $+ $1 $2].map{|s| "#{s}: #{eval("defined?(#{s})").inspect}"}
# $~: "global-variable"
# $&: "global-variable"
# $`: "global-variable"
# $': "global-variable"
# $+: "global-variable"
# $1: "global-variable"
# $2: nil
```

I would assume that `defined?($~)` should be nil if the others are nil.  Alternatively, it would make sense for `defined?` to always return `global-variable` for `$& $' $~ $(backquote)`.  `$!` is similar to the regexp globals in terms of scoping, and it returns `global-variable` even if not set.

I checked and `defined?($+)` is `nil` if the backref has no captures.  I don't think we can change the behavior of `defined?($+)` or `defined?($1)` without significantly breaking backwards compatibility.

Also kind of weird is that `defined?` treats aliases of these global variables differently than it treats the variables themselves:

```ruby
defined?($&) # nil
alias $MATCH $&
defined?($&) # nil
defined?($MATCH) # "global-variable"
```

I would think we would want `defined?` to treat global variable aliases the same as the global variables they alias.

----------------------------------------
Bug #11304: [PATCH] Kernel.global_variables should observe $~.
https://bugs.ruby-lang.org/issues/11304#change-79134

* Author: 0x0dea (D.E. Akers)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
The added complexity does impact performance, but the difference is negligible, and the method should return what it says it does.

---Files--------------------------------
global_variables_captures.patch (1.85 KB)


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