ruby - Return self (rather than nil) from Hash#[] when key doesn't exist

Question

Typically when an element is passed into a hash with no matching key, the hash returns nil.

hsh = {1 => "one", 2 => "two"}
hsh[3] #=> nil

I want to form a hash that returns the value passed into it if there is no match.

hsh[3] #=> 3

I'm guessing that a solution for this might involve a lambda of some kind...?

** Right now I'm using a clumsy solution for this that uses a conditional method to prevent non-matching keys from being passed into the hash..

Answer 1

如果您只想返回新值但不添加它们：

 h = Hash.new { |_hash, key| key }

要最初填充此哈希，您可以执行以下操作：

 h.merge( {1 => "one", 2 => "two"} )

如果哈希已经创建*：

 h.default_­proc = proc do |_hash,key|
     key
 end

#h[3]
#=> 3

*仅在 ruby​​ 1.9 及更高版本中

Answer 2

尝试这个：

hsh.default_proc = proc do |hash, key|
  hash[key] = key
end

只返回密钥，这是一个微不足道的改变：

hsh.default_proc = proc do |hash, key|
  key
end