从Ruby 2.3开始，%遵循通过default=设置的默认值：

hash = {name: 'Tim', city: 'Lahore'}
hash.default = ''

'hello %{name}, today is %{day}' % hash
#=> "hello Tim, today is "

或通过default_proc=设置的动态默认值：

hash = {name: 'Tim', city: 'Lahore'}
hash.default_proc = proc { |h, k| "%{#{k}}" }

'hello %{name}, today is %{day}' % hash
#=> "hello Tim, today is %{day}"

请注意，只有缺少的密钥，即:day被传递到proc。因此，它不知道您在格式字符串中使用的是%{day}还是%<day>s，这可能会导致不同的输出：

'hello %{name}, today is %<day>s' % hash
#=> "hello Tim, today is %{day}"

你可以设置一个默认的哈希值：

h = {name: "Tim", city: "Lahore"}
h.default = "No key"
p "hello %{name}, today is %{day}" % h #=>"hello Tim, today is No key"

我有一个带空格的散列键，它在将键转换为符号后工作。
Hash with String keys（它返回了一个插值错误）：

hash = {"First Name" => "Allama", "Last Name" => "Iqbal"}

将散列键转换为Symbols对我来说很有效：

hash = {:"First Name" => "Allama", :"Last Name" => "Iqbal"}
hash.default = ''

'The %{First Name} %{Last Name} was a great poet.' % hash

// The Allama Iqbal was a great poet.

我知道这是旧的，但我最终使我的需要实用程序。这是我的Gist https://gist.github.com/Genkilabs/71b479e1b1300a581a85e047db1cbb43

#@param String with %{key} interpolation fields
  #@param Hash or Rails Model
  #@returns String original with any keys replaced if they are in the hash, others ignored
  def self.interpolate str, obj
    #For the hash, we need to re-key the hash to be sure, and add default to skip missing interpolations
    safe_hash = (defined?(obj.attributes) ? obj.attributes : obj.to_h).symbolize_keys
    safe_hash.default_proc = proc{|h, k| "%{#{k}}" }
    #On the string side, safeguard any place ther is a symbol inside an interpolated field
    str.gsub('%{:', '%{') % safe_hash
  end