'keys.each'和'each_key'有什么区别？

Question

迭代如下所示的哈希:

hash.keys.each do |key|
  process_key(key)
end

Rubocop宣称我应该使用:

each_key

代替:

keys.each

keys.each和之间的"关键"区别是each_key什么？

Answer 1

由于性能，Rubocop希望您根据您评估的代码来遵循此要求。使用大型数据集会变得很明显。这是文档：https : //github.com/bbatsov/rubocop/blob/master/manual/cops_performance.md#performancehasheachmethods

我还发现有人编写了一个基准测试此基准：https : //gist.github.com/jodosha/8ca2bee6137be94e9dcb

我对其进行了一些修改并在我的系统上运行：

Warming up --------------------------------------
         string each   128.742k i/100ms
         string keys   114.523k i/100ms
     string each_key   134.279k i/100ms
         symbol each   128.838k i/100ms
         symbol keys   109.398k i/100ms
     symbol each_key   132.021k i/100ms
Calculating -------------------------------------
         string each      2.053M (± 4.0%) i/s -     10.299M in   5.026890s
         string keys      1.864M (± 1.4%) i/s -      9.391M in   5.039759s
     string each_key      2.224M (± 5.5%) i/s -     11.145M in   5.032201s
         symbol each      2.082M (± 1.0%) i/s -     10.436M in   5.013145s
         symbol keys      1.815M (± 2.1%) i/s -      9.080M in   5.004690s
     symbol each_key      2.240M (± 1.9%) i/s -     11.222M in   5.012184s

Comparison:
     symbol each_key:  2239720.0 i/s
     string each_key:  2224205.1 i/s - same-ish: difference falls within error
         symbol each:  2081895.2 i/s - 1.08x  slower
         string each:  2052884.9 i/s - 1.09x  slower
         string keys:  1863740.5 i/s - 1.20x  slower
         symbol keys:  1815131.1 i/s - 1.23x  slower

链接方法将比使用内置方法（在这种情况下）要慢，后者使用一个特殊的枚举器完成任务。语言创建者把它放在这里是有原因的，也是它的惯用语。