Add String#sub! vs String#gub! vs String#[]=

Closes #41

Author: sshaw

README.md

@@ -732,6 +732,36 @@ Comparison:
          String#gsub:   516604.2 i/s - 3.60x slower
 ```
 
+##### `String#sub!` vs `String#gsub!` vs `String#[]=` [code](code/string/sub!-vs-gsub!-vs-[]=.rb)
+
+```
+$ ruby -v code/string/sub\!-vs-gsub\!-vs-\[\]\=.rb
+ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin14]
+
+Calculating -------------------------------------
+  String#['string']=    74.512k i/100ms
+ String#sub!'string'    52.801k i/100ms
+String#gsub!'string'    34.480k i/100ms
+  String#[/regexp/]=    55.325k i/100ms
+ String#sub!/regexp/    45.770k i/100ms
+String#gsub!/regexp/    27.665k i/100ms
+-------------------------------------------------
+  String#['string']=      1.215M (± 6.2%) i/s -      6.110M
+ String#sub!'string'    752.731k (± 6.2%) i/s -      3.749M
+String#gsub!'string'    481.183k (± 4.4%) i/s -      2.414M
+  String#[/regexp/]=    840.615k (± 5.3%) i/s -      4.205M
+ String#sub!/regexp/    663.075k (± 7.8%) i/s -      3.295M
+String#gsub!/regexp/    342.004k (± 7.5%) i/s -      1.715M
+
+Comparison:
+  String#['string']=:  1214845.5 i/s
+  String#[/regexp/]=:   840615.2 i/s - 1.45x slower
+ String#sub!'string':   752731.4 i/s - 1.61x slower
+ String#sub!/regexp/:   663075.3 i/s - 1.83x slower
+String#gsub!'string':   481183.5 i/s - 2.52x slower
+String#gsub!/regexp/:   342003.8 i/s - 3.55x slower
+```
+
 ##### `attr_accessor` vs `getter and setter` [code](code/general/attr-accessor-vs-getter-and-setter.rb)
 
 > https://www.omniref.com/ruby/2.2.0/files/method.h?#annotation=4081781&line=47

code/string/sub!-vs-gsub!-vs-[]=.rb

@@ -0,0 +1,44 @@
+require "benchmark/ips"
+
+URL = "http://www.thelongestlistofthelongeststuffatthelongestdomainnameatlonglast.com/wearejustdoingthistobestupidnowsincethiscangoonforeverandeverandeverbutitstilllookskindaneatinthebrowsereventhoughitsabigwasteoftimeandenergyandhasnorealpointbutwehadtodoitanyways.html"
+
+def fast
+  s = URL.dup
+  s["http://"] = ""
+end
+
+def slow_1
+  s = URL.dup
+  s.sub! "http://", ""
+end
+
+def slow_2
+  s = URL.dup
+  s.gsub! "http://", ""
+end
+
+def slow_3
+  s = URL.dup
+  s[%r{http://}] = ""
+end
+
+def slow_4
+  s = URL.dup
+  s.sub! %r{http://}, ""
+end
+
+def slow_5
+  s = URL.dup
+  s.gsub! %r{http://}, ""
+end
+
+
+Benchmark.ips do |x|
+  x.report("String#['string']=")   { fast   }
+  x.report("String#sub!'string'")  { slow_1 }
+  x.report("String#gsub!'string'") { slow_2 }
+  x.report("String#[/regexp/]=")   { slow_3 }
+  x.report("String#sub!/regexp/")  { slow_4 }
+  x.report("String#gsub!/regexp/") { slow_5 }
+  x.compare!
+end