String#respond_to? vs ::method_defined?

benchmark.rb

random_strings = (1..100_000).map { ('a'..'z').to_a.shuffle[0, 8].join }; nil

Benchmark.bm do |x|
  x.report { random_strings.each { |s| s.respond_to?(s) } }
  x.report { random_strings.each { |s| String.method_defined?(s) } }
end

# =>       user     system      total        real
# =>   0.042596   0.001688   0.044284 (  0.044286)
# =>   0.011542   0.000012   0.011554 (  0.011556)