Fastest way to check if a string matches a regexp in ruby?

Starting with Ruby 2.4.0, you may use RegExp#match?:

pattern.match?(string)

Regexp#match? is explicitly listed as a performance enhancement in the release notes for 2.4.0, as it avoids object allocations performed by other methods such as Regexp#match and =~:

Regexp#match?
Added Regexp#match?, which executes a regexp match without creating a back reference object and changing $~ to reduce object allocation.