Ruby

This comes from a discussion on a PR on Sidekiq: https://github.com/mperham/sidekiq/pull/4303

This benchmark:

# frozen_string_literal: true require "benchmark/ips" def deep_dup_case(obj) case obj when Integer, Float, TrueClass, FalseClass, NilClass obj when String obj.dup when Array obj.map { |e| deep_dup_case(e) } when Hash duped = obj.dup duped.each_pair do |key, value| duped[key] = deep_dup_case(value) end else obj.dup end end def deep_dup_if(obj) if Integer === obj || Float === obj || TrueClass === obj || FalseClass === obj || NilClass === obj obj elsif String === obj obj.dup elsif Array === obj obj.map { |e| deep_dup_if(e) } elsif Hash === obj duped = obj.dup duped.each_pair do |key, value| duped[key] = deep_dup_if(value) end duped else obj.dup end end obj = { "class" => "FooWorker", "args" => [1, 2, 3, "foobar"], "jid" => "123987123" } Benchmark.ips do |x| x.report("deep_dup_case") do deep_dup_case(obj) end x.report("deep_dup_if") do deep_dup_if(obj) end x.compare! end 

gives in MRI 2.6.5:

Warming up -------------------------------------- deep_dup_case 37.767k i/100ms deep_dup_if 41.802k i/100ms Calculating ------------------------------------- deep_dup_case 408.046k (± 0.9%) i/s - 2.077M in 5.090997s deep_dup_if 456.657k (± 0.9%) i/s - 2.299M in 5.035040s Comparison: deep_dup_if: 456657.4 i/s deep_dup_case: 408046.1 i/s - 1.12x slower 

It seems @tenderlovemaking (Aaron Patterson) already noticed this a while ago due to missing inline caches for case, but the performance bug seems to still remain:
https://youtu.be/b77V0rkr5rk?t=1442

Do you think this could be fixed in MRI?
AFAIK both JRuby and TruffleRuby support inline cached === calls in case/when.

I think the code with case is more idiomatic and readable and should be preferred to if, and this performance issue makes that less clear.