use defined?(xxx) (tastes great, less filling)

- #502

benchmarks/respond_to_v_defined.rb

@@ -0,0 +1,72 @@
+require 'benchmark'
+
+n = 1_000_000
+
+puts "Kernel.respond_to?(:warn)"
+
+Benchmark.benchmark do |bm|
+  3.times do
+    bm.report do
+      n.times do
+       Kernel.respond_to?(:warn)
+      end
+    end
+  end
+end
+
+puts "defined?(warn)"
+
+Benchmark.benchmark do |bm|
+  3.times do
+    bm.report do
+      n.times do
+        defined?(warn)
+      end
+    end
+  end
+end
+
+puts "Kernel.respond_to?(:foo)"
+
+Benchmark.benchmark do |bm|
+  3.times do
+    bm.report do
+      n.times do
+        Kernel.respond_to?(:foo)
+      end
+    end
+  end
+end
+
+puts "defined?(foo)"
+
+Benchmark.benchmark do |bm|
+  3.times do
+    bm.report do
+      n.times do
+        defined?(foo)
+      end
+    end
+  end
+end
+
+# $ ruby benchmarks/respond_to_v_defined.rb 
+# Kernel.respond_to?(:warn)
+#    0.190000   0.000000   0.190000 (  0.206502)
+#    0.190000   0.000000   0.190000 (  0.197547)
+#    0.190000   0.000000   0.190000 (  0.189731)
+# defined?(warn)
+#    0.190000   0.000000   0.190000 (  0.187334)
+#    0.180000   0.000000   0.180000 (  0.201078)
+#    0.190000   0.000000   0.190000 (  0.202295)
+# Kernel.respond_to?(:foo)
+#    0.250000   0.010000   0.260000 (  0.255003)
+#    0.240000   0.000000   0.240000 (  0.247376)
+#    0.250000   0.000000   0.250000 (  0.251196)
+# defined?(foo)
+#    0.100000   0.000000   0.100000 (  0.104748)
+#    0.110000   0.000000   0.110000 (  0.107250)
+#    0.110000   0.000000   0.110000 (  0.107990)
+#
+# defined is consistently faster, but it takes 1,000,000 x to have a meaningful
+# diff

lib/rspec/core.rb

@@ -1,4 +1,4 @@
-if Kernel.respond_to?(:require_relative)
+if defined?(require_relative)
   def require_rspec(path)
     require_relative path
   end