Add inheritance check

README.md

@@ -188,6 +188,23 @@ Comparison:
          Kernel loop:        0.2 i/s - 2.41x slower
 ```
 
+##### `ancestors.include?` vs `<=` [code](code/general/inheritance-check.rb)
+
+```
+$ ruby -vW0 code/general/inheritance-check.rb
+ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
+Warming up --------------------------------------
+  less than or equal    66.992k i/100ms
+  ancestors.include?    16.943k i/100ms
+Calculating -------------------------------------
+  less than or equal      1.250M (± 6.4%) i/s -      6.230M in   5.006896s
+  ancestors.include?    192.603k (± 4.8%) i/s -    965.751k in   5.025917s
+
+Comparison:
+  less than or equal:  1249606.0 i/s
+  ancestors.include?:   192602.9 i/s - 6.49x  slower
+```
+
 #### Method Invocation
 
 ##### `call` vs `send` vs `method_missing` [code](code/method/call-vs-send-vs-method_missing.rb)

code/general/inheritance-check.rb

@@ -0,0 +1,38 @@
+require 'benchmark/ips'
+
+# You may ask: 'Is there a project that still using `ancestors.include?`?'
+# By quick searching, I found the following popular repositories are still using it:
+# - rake 
+#   - https://github.com/ruby/rake/blob/7d0c08fe4e97083a92d2c8fc740cb421fd062117/lib/rake/task_manager.rb#L28
+# - warden 
+#   - https://github.com/hassox/warden/blob/090ed153dbd2f5bf4a1ca672b3018877e21223a4/lib/warden/strategies.rb#L16
+# - metasploit-framework
+#   - https://github.com/rapid7/metasploit-framework/blob/cac890a797d0d770260074dfe703eb5cfb63bd46/lib/msf/core/payload_set.rb#L239
+#   - https://github.com/rapid7/metasploit-framework/blob/cb82015c8782280d964e222615b54c881bd36bbe/lib/msf/core/exploit.rb#L1440
+# - hanami
+#   - https://github.com/hanami/hanami/blob/506a35e5262939eb4dce9195ade3268e19928d00/lib/hanami/components/routes_inspector.rb#L54
+#   - https://github.com/hanami/hanami/blob/aec069b602c772e279aa0a7f48d1a04d01756ee3/lib/hanami/configuration.rb#L114
+raise unless Object.ancestors.include?(Kernel)
+raise unless (Object <= Kernel)
+
+def fast
+  (Class <= Class)
+  (Class <= Module)
+  (Class <= Object)
+  (Class <= Kernel)
+  (Class <= BasicObject)
+end
+
+def slow
+  Class.ancestors.include?(Class)
+  Class.ancestors.include?(Module)
+  Class.ancestors.include?(Object)
+  Class.ancestors.include?(Kernel)
+  Class.ancestors.include?(BasicObject)
+end
+
+Benchmark.ips do |x|
+  x.report('less than or equal') { fast }
+  x.report('ancestors.include?') { slow }
+  x.compare!
+end