ruby-on-rails - 在 Ruby 数组中使用返回枚举器的方法的正确方法是什么？

Question

Ruby array 中的许多方法在没有参数或 block 的情况下调用时返回枚举器(index、keep_if、each、drop_while 等等)。

• 什么时候适合使用这种形式的方法，而不是用 block 调用它们？

Answer 1

从文档到 Enumerator :

Most methods have two forms: a block form where the contents are evaluated for each item in the enumeration, and a non-block form which returns a new Enumerator wrapping the iteration.

This allows you to chain Enumerators together. For example, you can map a list’s elements to strings containing the index and the element as a string via:

puts %w[foo bar baz].map.with_index {|w,i| "#{i}:#{w}" }
# => ["0:foo", "1:bar", "2:baz"]

An Enumerator can also be used as an external iterator. For example, Enumerator#next returns the next value of the iterator or raises StopIteration if the Enumerator is at the end.

e = [1,2,3].each   # returns an enumerator object.
puts e.next   # => 1
puts e.next   # => 2
puts e.next   # => 3
puts e.next   # raises StopIteration

很抱歉复制粘贴，但我无法解释得更好。