Add benchmark for Hash#dig vs #[] vs #fetch

Author: dideler

README.md

@@ -591,6 +591,32 @@ Comparison:
   Hash#fetch, string:  3981166.5 i/s - 1.89x slower
 ```
 
+##### `Hash#dig` vs `Hash#[]` vs `Hash#fetch` [code](code/hash/dig-vs-[]-fetch.rb)
+
+```
+$ ruby -v code/hash/dig-vs-\[\]-vs-fetch.rb
+ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]
+Warming up --------------------------------------
+            Hash#dig   144.192k i/100ms
+             Hash#[]   148.853k i/100ms
+    Hash#[] fallback   149.761k i/100ms
+          Hash#fetch   132.257k i/100ms
+ Hash#fetch fallback   120.420k i/100ms
+Calculating -------------------------------------
+            Hash#dig      6.253M (± 5.9%) i/s -     31.145M
+             Hash#[]      6.733M (± 5.9%) i/s -     33.641M
+    Hash#[] fallback      6.209M (± 5.7%) i/s -     31.001M
+          Hash#fetch      4.500M (± 5.0%) i/s -     22.484M
+ Hash#fetch fallback      3.330M (± 4.7%) i/s -     16.618M
+
+Comparison:
+             Hash#[]:  6732624.6 i/s
+            Hash#dig:  6252809.1 i/s - same-ish: difference falls within error
+    Hash#[] fallback:  6209365.5 i/s - same-ish: difference falls within error
+          Hash#fetch:  4499831.0 i/s - 1.50x slower
+ Hash#fetch fallback:  3330397.7 i/s - 2.02x slower
+```
+
 ##### `Hash[]` vs `Hash#dup` [code](code/hash/bracket-vs-dup.rb)
 
 Source: http://tenderlovemaking.com/2015/02/11/weird-stuff-with-hashes.html

code/hash/dig-vs-[]-vs-fetch.rb

@@ -0,0 +1,27 @@
+require 'benchmark/ips'
+
+h = { a: { b: { c: { d: { e: "foo" } } } } }
+
+Benchmark.ips do |x|
+  x.report 'Hash#dig' do
+    h.dig(:a, :b, :c, :d, :e)
+  end
+
+  x.report 'Hash#[]' do
+    h[:a][:b][:c][:d][:e]
+  end
+
+  x.report 'Hash#[] fallback' do
+    ((((h[:a] || {})[:b] || {})[:c] || {})[:d] || {})[:e]
+  end
+
+  x.report 'Hash#fetch' do
+    h.fetch(:a).fetch(:b).fetch(:c).fetch(:d).fetch(:e)
+  end
+
+  x.report 'Hash#fetch fallback' do
+    h.fetch(:a, {}).fetch(:b, {}).fetch(:c, {}).fetch(:d, {}).fetch(:e, nil)
+  end
+
+  x.compare!
+end