Ruby中的默认哈希值(Rubykoans.com – > about_hashes.rb)

我从 RubyKoans开始经历about_hashes.rb.1练习让我感到困惑：

def test_default_value
    hash1 = Hash.new
    hash1[:one] = 1

    assert_equal 1,hash1[:one] #ok
    assert_equal nil,hash1[:two] #ok

    hash2 = Hash.new("dos")
    hash2[:one] = 1

    assert_equal 1,hash2[:one] #ok
    assert_equal "dos",hash2[:two] #hm?
  end

我的猜测是Hash.new(“dos”)使“dos”成为所有不存在键的默认答案.我对吗？

解决方法

是的,你是对的,看起来ruby公司有一个错误,hash2 [：two]将返回“dos”

看一下Hash.new方法文档

new → new_hash
new(obj) → new_hash
new {|hash,key| block } → new_hash

Returns a new,empty hash. If this hash is subsequently accessed by a
key that doesn’t correspond to a hash entry,the value returned
depends on the style of new used to create the hash. In the first
form,the access returns nil. If obj is specified,this single object
will be used for all default values. If a block is specified,it will
be called with the hash object and the key,and should return the
default value. It is the block’s responsibility to store the value in
the hash if required.

旁注：在这种情况下,您可以通过运行实际代码或在irb或pry中执行几行来确认您的期望(我建议使用pry).