迭代哈希

Hash 包含 Enumerable 模块，它提供了几种迭代方法，例如：Enumerable#each，Enumerable#each_pair，Enumerable#each_key 和 Enumerable#each_value。

.each 和 .each_pair 遍历每个键值对：

h = { "first_name" => "John", "last_name" => "Doe" }
h.each do |key, value|
    puts "#{key} = #{value}"
end

# => first_name = John
#    last_name = Doe

.each_key 仅迭代密钥：

h = { "first_name" => "John", "last_name" => "Doe" }
h.each_key do |key|
  puts key
end

# => first_name
#    last_name

.each_value 仅迭代值：

h = { "first_name" => "John", "last_name" => "Doe" }
h.each_value do |value|
    puts value
end

# => John
#    Doe

.each_with_index 迭代元素并提供迭代的索引：

h = { "first_name" => "John", "last_name" => "Doe" }
h.each_with_index do |(key, value), index|
    puts "index: #{index} | key: #{key} | value: #{value}"
end

# => index: 0 | key: first_name | value: John
#    index: 1 | key: last_name | value: Doe