From 57890c381c09779d960a5242819acb32fdf2d53d Mon Sep 17 00:00:00 2001
From: Jonathan Hefner <jonathan.hefner@gmail.com>
Date: Tue, 24 May 2016 18:43:37 -0500
Subject: [PATCH] Add String#start_with? vs String#[].==

---
 README.md                                 | 18 ++++++++++++
 code/string/start_with-vs-substring-==.rb | 34 +++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100755 code/string/start_with-vs-substring-==.rb

diff --git a/README.md b/README.md
index ae7c86a..b63533a 100644
--- a/README.md
+++ b/README.md
@@ -884,6 +884,24 @@ Comparison:
            String#=~:   891124.1 i/s - 3.30x slower
 ```
 
+##### `String#start_with?` vs `String#[].==` [code](code/string/start_with-vs-substring-==.rb)
+
+```
+ruby 2.2.4p230 (2015-12-16 revision 53155) [i386-cygwin]
+
+Calculating -------------------------------------
+  String#start_with?    739.364k (± 0.5%) i/s -      3.720M in   5.031116s
+    String#[0, n] ==    346.112k (± 0.2%) i/s -      1.753M in   5.063586s
+   String#[RANGE] ==    318.284k (± 0.2%) i/s -      1.612M in   5.066202s
+   String#[0...n] ==    220.535k (± 0.1%) i/s -      1.110M in   5.033769s
+
+Comparison:
+  String#start_with?:   739364.0 i/s
+    String#[0, n] ==:   346112.1 i/s - 2.14x slower
+   String#[RANGE] ==:   318283.6 i/s - 2.32x slower
+   String#[0...n] ==:   220534.9 i/s - 3.35x slower
+```
+
 ##### `Regexp#===` vs `String#match` vs `String#=~` [code ](code/string/===-vs-=~-vs-match.rb)
 
 > :warning: <br>
diff --git a/code/string/start_with-vs-substring-==.rb b/code/string/start_with-vs-substring-==.rb
new file mode 100755
index 0000000..7008d42
--- /dev/null
+++ b/code/string/start_with-vs-substring-==.rb
@@ -0,0 +1,34 @@
+require 'benchmark/ips'
+
+PREFIX = '_'
+STRINGS = (0..9).map{|n| "#{PREFIX if n.odd?}#{n}" }
+
+START_WITH = STRINGS.each_index.map do |i|
+  "STRINGS[#{i}].start_with?(PREFIX)"
+end.join(';')
+
+EQL_USING_LENGTH = STRINGS.each_index.map do |i|
+  # use `eql?` instead of `==` to prevent warnings
+  "STRINGS[#{i}][0, PREFIX.length].eql?(PREFIX)"
+end.join(';')
+
+RANGE = 0...PREFIX.length
+
+EQL_USING_RANGE_PREALLOC = STRINGS.each_index.map do |i|
+  # use `eql?` instead of `==` to prevent warnings
+  "STRINGS[#{i}][RANGE].eql?(PREFIX)"
+end.join(';')
+
+EQL_USING_RANGE = STRINGS.each_index.map do |i|
+  # use `eql?` instead of `==` to prevent warnings
+  "STRINGS[#{i}][0...PREFIX.length].eql?(PREFIX)"
+end.join(';')
+
+
+Benchmark.ips do |x|
+  x.report('String#start_with?', START_WITH)
+  x.report('String#[0, n] ==', EQL_USING_LENGTH)
+  x.report('String#[RANGE] ==', EQL_USING_RANGE_PREALLOC)
+  x.report('String#[0...n] ==', EQL_USING_RANGE)
+  x.compare!
+end