ms-ati · August 10, 2017 19:51 · Aug 10, 2017
diff --git a/ruby_fast_case_when_set.rb b/ruby_fast_case_when_set.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+#
+# What's the fast way to find a constant set of values in a ruby case statement?
+#
+require "benchmark/ips"
+require "set"
+
+# Provides a `===` operator for a Set
+class SetCaseEq
+  def initialize(enum)
+    @set = enum.to_set
+  end
+
+  def ===(val)
+    @set.include?(val)
+  end
+end
+
+NUM = 1_000
+ARR = Array.new(NUM) { rand(1..100) }.freeze
+SET = SetCaseEq.new(ARR)
+
+def slow
+  ARR.map do |n|
+    case n
+    when 1
+      "a"
+    when 42
+      "b"
+    when *ARR
+      "c"
+    else
+      nil
+    end
+  end
+end
+
+def fast
+  ARR.map do |n|
+    case n
+    when 1
+      "a"
+    when 42
+      "b"
+    when SET
+      "c"
+    else
+      nil
+    end
+  end
+end
+
+raise "doesn't work" if slow != fast
+
+Benchmark.ips do |x|
+  x.report("Array splat")  { slow }
+  x.report("Set#include?") { fast }
+  x.compare!
+end
diff --git a/ruby_fast_case_when_set_results.md b/ruby_fast_case_when_set_results.md
@@ -0,0 +1,13 @@
+```
+$ ruby ruby_fast_case_when_set.rb
+Warming up --------------------------------------
+         Array splat    21.000  i/100ms
+        Set#include?   425.000  i/100ms
+Calculating -------------------------------------
+         Array splat    226.534  (± 5.3%) i/s -      1.134k in   5.019588s
+        Set#include?      4.282k (± 0.9%) i/s -     21.675k in   5.062326s
+
+Comparison:
+        Set#include?:     4282.0 i/s
+         Array splat:      226.5 i/s - 18.90x  slower
+```
No results found