使用 Ruby 将字符串的开头或结尾与子字符串进行比较的最快方法是什么？

Question

对字符串进行切片"Hello world!"[0, 5] == 'Hello' 是Ruby 中的一个常用习惯用法，用于将字符串的第一个或最后n 个字符与另一个字符串进行比较。正则表达式也可以做到。还有start_with? 和end_with? 也可以做到这一点。

我应该使用哪个速度最快？

Answer 1

考虑这些测试：

require 'fruity'

STR = '!' + ('a'..'z').to_a.join # => "!abcdefghijklmnopqrstuvwxyz"

单个字符开始字符串的结果：

compare do
  _slice { STR[0] == '!' }
  _start_with { STR.start_with?('!') }
  _regex { !!STR[/^!/] }
end

# >> Running each test 32768 times. Test will take about 1 second.
# >> _start_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

多个字符开始一个字符串的结果：

compare do
  _slice { STR[0..4] == '!abcd' }
  _start_with { STR.start_with?('!abcd') }
  _regex { !!STR[/^!abcd/] }
end

# >> Running each test 32768 times. Test will take about 2 seconds.
# >> _start_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

单个字符结束字符串的结果：

compare do
  _slice { STR[-1] == 'z' }
  _end_with { STR.end_with?('z') }
  _regex { !!STR[/z$/] }
end

# >> Running each test 32768 times. Test will take about 2 seconds.
# >> _end_with is faster than _slice by 2x ± 1.0
# >> _slice is faster than _regex by 2x ± 1.0

多个字符结束一个字符串的结果：

compare do
  _slice { STR[-5..-1] == 'vwxyz' }
  _end_with { STR.end_with?('vwxyz') }
  _regex { !!STR[/vwxyz$/] }
end

# >> Running each test 16384 times. Test will take about 1 second.
# >> _end_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

因此，为了清晰和快速，start_with? 和 end_with? 应该是我们的首选。如果我们需要使用模式，那么切片或使用正则表达式是显而易见的选择。