Ruby

While working on TruffleRuby's regexp variables implementation I found the following behaviour when comparing our behaviour with MRI 2.3.5 and 2.5.0.

Some core methods such as String#scan take an optional block argument, and if this is a literal block then each time it is yielded to the $~ variable will have been set. However, if the block is a proc that was not defined in the caller's scope then $~ does not appear to get set or is inaccessible.

The following test script demonstrates the problem.

class ScanChecker def block Proc.new do puts "$~ is #{$~}" end end end puts 'Checking with literal block.' 'hello'.scan(/l/) do puts "$~ is #{$~}" end puts 'Checking with a Proc from same scope' my_proc = Proc.new do puts "$~ is #{$~}" end 'hello'.scan(/l/, &my_proc) puts 'Checking with a Proc.' checker = ScanChecker.new 'hello'.scan(/l/, &checker.block) 

I would have expected the $~ to be set in all cases, but I'm not sure if that is the intended behaviour.