Prefer grep/grep_v

[marcandre]

The following code has 3 anti-patterns:

def self.tokens(pattern)
   pattern.scan(TOKEN).reject { |token| token =~ /\A#{SEPARATORS}\Z/ }
end

This issue is to identify that enum.reject { |x| x.match? regexp } should be enum.grep_v(regexp). Same with select vs grep.

See: rubocop/rubocop-ast#65

[fatkodima]

I have run a quick benchmark. Looks like grep/grep_v are not so nice, while simplifying code a bit.

Benchmark code

# frozen_string_literal: true

require 'bundler/inline'

gemfile(true) do
  gem 'benchmark-ips'
  gem 'benchmark-memory'
end

arr = ['foobar', 'foobaz', 'bazquux']

REGEXP = /foo/

def select_match(arr)
  arr.select { |e| e.match?(REGEXP) }
end

def grep(arr)
  arr.grep(REGEXP)
end

Benchmark.ips do |x|
  x.report("select.match?")  { select_match(arr) }
  x.report("grep")           { grep(arr) }
  x.compare!
end

puts "********* MEMORY *********"

Benchmark.memory do |x|
  x.report("select.match?")  { select_match(arr) }
  x.report("grep")           { grep(arr) }
  x.compare!
end

Warming up --------------------------------------
       select.match?   159.869k i/100ms
                grep    56.192k i/100ms
Calculating -------------------------------------
       select.match?      1.561M (± 6.5%) i/s -      7.834M in   5.044218s
                grep    565.201k (± 1.6%) i/s -      2.866M in   5.071747s

Comparison:
       select.match?:  1561061.6 i/s
                grep:   565201.5 i/s - 2.76x  (± 0.00) slower

********* MEMORY *********
Calculating -------------------------------------
       select.match?    40.000  memsize (     0.000  retained)
                         1.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
                grep   208.000  memsize (     0.000  retained)
                         2.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
       select.match?:         40 allocated
                grep:        208 allocated - 5.20x more

[marcandre]

Kudos for checking that @fatkodima I would not have thought so. It makes some sense, because grep calls === which is =~ for Regexp. This should be optimized by Ruby... I'll write an issue (unless you'd prefer doing that yourself)?

[fatkodima]

Please, do 👍

[fatkodima]

@marcandre
So do you think it is worth implementing, due to https://bugs.ruby-lang.org/issues/17030, but making it disabled by default?
grep/grep_v can be also extended by Enumerable#{any?,all?,none?,one?} with regexp argument.

[marcandre]

Sure. What would be worth implementing is fixing 17030 :-) IIUC, Matz is ok with optimizing this