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 (¡Þ 0.0%) i/s - 3.000 in 6.759200s
new_csv_shift 0.479 (¡Þ 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 (¡Þ 3.8%) i/s - 9.179M in 5.006568s
a.start_with?(b) 3.183M (¡Þ 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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