Issue #8110 has been updated by headius (Charles Nutter).


Crazy idea: what if in the future you needed to set $~ to nil in order for it to be settable by downstream calls (e.g. regexp match)? It would eliminate a great deal of magic and treat those calls the same way we treat closures: if the variable has not been instantiated outside the nested scope/call, it's not available to be set.

e.g.

    def foo(regexp)
      "Hello, world?" =~ regexp # does not set backtrace
      $~ = nil
      "Hello, world?" =~ regexp # does set backtrace, same as a closure setting a non-local variable.
    end

Is this unreasonable?
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Feature #8110: Regex methods not changing global variables
https://bugs.ruby-lang.org/issues/8110#change-38488

Author: prijutme4ty (Ilya Vorontsov)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: next minor


It is useful to have methods allowing pattern matching without setting global variables. It can be very hard to understand where the problem is when you for example insert a string like `puts pat === my_str` and your program fails in a place which is far-far away from inserted place. This can happen due to replacing global variables of previous pattern match. I caught to this when placed pattern-match inside case-statement and shadowed global vars which were initially filled by match in when-statement.
For now one can extract pattern matching into another method thus defining method-scope for that variables. But sometimes it looks like an overkill. May be simple method like #match_globalsafe can prevent that kind of errors. At least when a programmer see such a method in a list of methods, he's warned that usual match can cause such problems.


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