Ruby Enumerable.each_with_index用法及代码示例

给定一个块，调用带有每个元素及其索引的块；返回 self ：

h = {}
(1..4).each_with_index {|element, i| h[element] = i } # => 1..4
h # => {1=>0, 2=>1, 3=>2, 4=>3}

h = {}
%w[a b c d].each_with_index {|element, i| h[element] = i }
# => ["a", "b", "c", "d"]
h # => {"a"=>0, "b"=>1, "c"=>2, "d"=>3}

a = []
h = {foo: 0, bar: 1, baz: 2}
h.each_with_index {|element, i| a.push([i, element]) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[0, [:foo, 0]], [1, [:bar, 1]], [2, [:baz, 2]]]

如果没有给出块，则返回 Enumerator 。