Ruby Regex: difference between new and union with a single regexp
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Ruby Regex: difference between new and union with a single regexp
I have simplified the examples. Say I have a string containing the code for a regex. I would like the regex to match a literal dot and thus I want it to be:
\.
So I create the following Ruby string:
"\\."
However when I use it with Regexp.union to create my regex, I get this:
irb(main):017:0> Regexp.union("\\.")
=> /\\\./
That will match a slash followed by a dot, not just a single dot. Compare the previous result to this:
irb(main):018:0> Regexp.new("\\.")
=> /\./
which gives the Regexp I want but without the needed union.
Could you explain why Ruby acts like that and how to make the correct union of regexes ? The context of utilization is that of importing JSON strings describing regexes and union-ing them in Ruby.
Passing a string to Regexp.union is designed to match that string literally. There is no need to escape it, Regexp.escape is already called internally.
Regexp.union(".")
#=> /\./
If you want to pass regular expressions to Regexp.union, don't use strings:
Regexp.union(Regexp.new("\\."))
#=> /\./
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