ruby - : "Hash.new takes a default value for the hash, which is the value of the hash for a nonexistent key"是什么意思

Question

我目前正在学习 Michael Hartl 的 Ruby on Rails 教程

不理解在 section 4.4.1 中找到的此语句的含义:

Hashes, in contrast, are different. While the array constructor Array.new takes an initial value for the array, Hash.new takes a default value for the hash, which is the value of the hash for a nonexistent key:

谁能帮忙解释一下这是什么意思？我不明白作者在本书这一部分的上下文中试图了解哈希与数组有何不同

Answer 1

您可以随时尝试 irb 或 rails console 中的代码以了解它们的含义。

Array.new
# => []

Array.new(7)
# => [nil, nil, nil, nil, nil, nil, nil]

h1 = Hash.new
h1['abc']
# => nil

h2 = Hash.new(7)
h2['abc']
# => 7