Add double splat operator vs merge

Author: Carlos Contreras

README.md

@@ -719,6 +719,23 @@ Comparison:
          Hash#merge!:    10653.3 i/s - 2.66x slower
 ```
 
+##### `Hash#merge` vs `Hash#**other` [code](code/hash/merge-vs-double-splat-operator.rb)
+
+```
+$ ruby -v merge-vs-double-splat-operator.rb
+ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin15]
+Warming up --------------------------------------
+        Hash#**other    64.624k i/100ms
+          Hash#merge    38.827k i/100ms
+Calculating -------------------------------------
+        Hash#**other    798.397k (± 6.9%) i/s -      4.007M in   5.053516s
+          Hash#merge    434.171k (± 4.5%) i/s -      2.174M in   5.018927s
+
+Comparison:
+        Hash#**other:   798396.6 i/s
+          Hash#merge:   434170.8 i/s - 1.84x  slower
+```
+
 ##### `Hash#merge` vs `Hash#merge!` [code](code/hash/merge-vs-merge-bang.rb)
 
 ```

code/hash/merge-vs-double-splat-operator.rb

@@ -0,0 +1,17 @@
+require 'benchmark/ips'
+
+def fast
+  h2 = { a: 'a' }
+  { one: 1, **h2 }
+end
+
+def slow
+  h2 = { a: 'a' }
+  { one: 1 }.merge(h2)
+end
+
+Benchmark.ips do |x|
+  x.report('Hash#**other') { fast }
+  x.report('Hash#merge') { slow }
+  x.compare!
+end