How to check if a named group exists in a MatchData object?

Question

ruby-1.9.2-p180 :003 > result = "test string".match(/(?<mtch>test)/) => #<MatchData "test" mtch:"test"> ruby-1.9.2-p180 :011 > result["mtch"] => "test" ruby-1.9.2-p180 :012 > result["fail"] IndexError: undefined group name reference: fail from (irb):12:in `[]' from (irb):12 from /Users/jeremysmith/.rvm/rubies/ruby-1.9.2-p180/bin/irb:16:in `<main>' 

There is no MatchData function to check for the existence of a named group. is there any other way to check?

Answer 1

 result.names.include? 'mtch' # => true result.names.include? 'fail' # => false 

Answer 2

 result["fail"] rescue false 

- one easy way. There are more elegant ways, but the rescue modifier is often useful, it is simple if you do not want to pay attention to excepted exceptions.

Answer 3

Just check if the data matches with p . In your case, the example already shows what you have.

 => #<MatchData "test" mtch:"test"> 

This means that the entire line that matches is equal to "test" , and the inventory of the name is (only) mtch . If he has a different name, it will be included in this form.