用常量值初始化 Ruby hash

Question

实际上我想在 chef 属性中使用这样的构造，我在其中用常量初始化一个结构并修改它

init_value = { "a" => { "b" => "c" } }
prepare = init_value
prepare["a"]["x"] = "y"

现在init_value也包含["a"]["x"] = "y"，所以当我准备一个新值

prepare = init_value
prepare["a"]["y"] = "x"

所以 prepare["a"] 包含键 ["b", "x", "y"].

如何在不引用常量的情况下使用常量初始化准备，以便在最后一步中，prepare["a"] 仅包含两个键 ["b","y"]?

Answer 1

我想你在分配准备时想要 "deep copy" 的 init_value。

见： How do I copy a hash in Ruby?

Answer 2

摘自Rails 4.2.7

Object#deep_dup "Returns a deep copy of object if it’s duplicable. If it’s not duplicable, returns self."
Hash#deep_dup "Returns a deep copy of hash."
Array#deep_dup "Returns a deep copy of array."

实施：

class Object
  def duplicable?
    true
  end
  def deep_dup
    duplicable? ? dup : self
  end
end 

class Hash
   def deep_dup
     each_with_object(dup) do |(key, value), hash|
       hash[key.deep_dup] = value.deep_dup
     end
  end
end

class Array
  def deep_dup
    map { |it| it.deep_dup }
  end
end

# Not duplicable? 
# if ruby version < 2.0 also add Class and Module as they were not duplicable until 2.0
[Method, Symbol, FalseClass, TrueClass, NilClass, Numeric, BigDecimal].each do |m|
  m.send(:define_method, :duplicable?, ->{false})
end

然后你可以为 init_value 使用一个方法，这样 deep_dup 总是被调用，你就不会不小心忘记

#since you asked for a constant
INIT_VALUE = { "a" => { "b" => "c" } }.freeze

def init_value 
  INIT_VALUE.deep_dup 
end

这样的用法

prepare = init_value
prepare["a"]["x"] = "y"

prepare2 = init_value
prepare2["a"]["y"] = "x"

prepare
#=> {"a"=>{"b"=>"c", "x"=>"y"}}
prepare2
#=> {"a"=>{"b"=>"c", "y"=>"x"}}

Answer 3

您可以将初始哈希移动到一个方法中。这样，该方法总是 returns a "fresh" hash:

def init_value
  {"a"=>{"b"=>"c"}}
end

prepare = init_value
prepare["a"]["x"] = "y"
prepare
#=> {"a"=>{"b"=>"c", "x"=>"y"}}

prepare = init_value
prepare["a"]["y"] = "x"
prepare
#=> {"a"=>{"b"=>"c", "y"=>"x"}}

用常量值初始化 Ruby hash

Initialize Ruby hash with a constant value

ruby

chef-infra

chef-attributes