Issue #12373 has been updated by Nobuyoshi Nakada.

Description updated

You can replace **`str1[-1] == str2`** with **`str1.end_with?(str2)`** too, three places.

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Bug #12373: Optimize CSV#shift
https://bugs.ruby-lang.org/issues/12373#change-58588

* Author: Yuki Kurihara
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.4.0dev (2016-05-11 trunk 54976) [x86_64-darwin15]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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I think that **`str1.start_with?(str2)`** is faster than **`str1[0] == str2`**.
Because **`str1.start_with?(str2)`** just call **`String#start_with?`**, But **`str1[0] == str2`** call **`String#[]`**, make new `String` object and call **`String#==`**.

(The patch is csv-shift.patch)

Benchmark results.

csv-benchmark.rb make temp CSV file and call **`CSV#each`** method(inner call **`CSV#shift`**)

~~~
$ ruby csv-benchmark.rb
Warming up --------------------------------------
       old_csv_shift     1.000  i/100ms
       new_csv_shift     1.000  i/100ms
Calculating -------------------------------------
       old_csv_shift      0.444  ( 0.0%) i/s -      3.000  in   6.759200s
       new_csv_shift      0.479  ( 0.0%) i/s -      3.000  in   6.264069s

Comparison:
       new_csv_shift:        0.5 i/s
       old_csv_shift:        0.4 i/s - 1.08x slower
~~~

string-start_with.rb is a micro benchmark for **`str1[0] == str2`** and **`str1.start_with?(str2)`**

~~~
$ ruby string-start_with.rb
Warming up --------------------------------------
           a[0] == b    90.881k i/100ms
    a.start_with?(b)   115.557k i/100ms
Calculating -------------------------------------
           a[0] == b      1.836M ( 3.8%) i/s -      9.179M in   5.006568s
    a.start_with?(b)      3.183M ( 4.2%) i/s -     15.947M in   5.018654s

Comparison:
    a.start_with?(b):  3183386.0 i/s
           a[0] == b:  1836263.5 i/s - 1.73x slower
~~~

Of course $ make test-all TESTS="test/csv/*" passed


---Files--------------------------------
csv-benchmark.rb (561 Bytes)
old_csv_shift.rb (5.1 KB)
new_csv_shift.rb (5.11 KB)
string-start_with.rb (215 Bytes)
csv-shift.patch (434 Bytes)


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