How do I convert hash keys to method names?

Question

This is my hash:

tempData = {"a" => 100, "here" => 200, "c" => "hello"}

I need to access the hash keys as a method like:

tempData.a #100
tempData.here # 200

Answer 1

You could just wrap up your hash in an OpenStruct:

require 'ostruct'
tempData = {"a" => 100, "here" => 200, "c" => "hello"}
os = OpenStruct.new tempData
os.a #=> 100
os.here #=> 200

If you really really wanted to, you could also monkey-patch the Hash class, but I'd advise against that:

class Hash
  def method_missing(m, *args, &blk)
    fetch(m) { fetch(m.to_s) { super } }
  end
end

tempData = {"a" => 100, "here" => 200, "c" => "hello"}
tempData.a #=> 100

Update: In my personal extensions library I added a Hash#to_ostruct method. This will recursively convert a hash into an OpenStruct including all nested hashes.

Answer 2

There is another way to do this.

JSON.parse(tempData.to_json, object_class: OpenStruct)

that will give object #<OpenStruct a=100, here=200, c="hello">

In this way nested hash also will be converted to OpenStruct Object

tempData = {a: { b: { c: 3}}, foo: 200, msg: 'test msg'}
obj = JSON.parse(tempData.to_json, object_class: OpenStruct)

Now we are able to call

obj.a.b.c # 3
obj.foo # 200
obj.msg # 'test msg'

Hope this will help someone.

Answer 3

Alternatively, if it’s just a small script it might be more convenient to just extend Hash itself

class Hash
  def method_missing sym,*
    fetch(sym){fetch(sym.to_s){super}}
  end
end

method_missing is a magic method that is called whenever your code tries to call a method that does not exist. Ruby will intercept the failing call at run time and let you handle it so your program can recover gracefully. The implementation above tries to access the hash using the method name as a symbol, the using the method name as a string, and eventually fails with Ruby's built-in method missing error.

NB for a more complex script, where adding this behavior might break other third-party gems, you might alternatively use a module and extend each instance

module H
  def method_missing sym,*
    fetch(sym){fetch(sym.to_s){super}}
  end
end

the = { answer: 42 }
the.extend(H)
the.answer # => 42

and for greater convenience you can even propagate the module down to nested hashes

module H
  def method_missing sym,*
    r = fetch(sym){fetch(sym.to_s){super}}
    Hash === r ? r.extend(H) : r
  end
end 

the = { answer: { is: 42 } }
the.extend(H)
the.answer.is # => 42

Answer 4

If the hash is inside a module, you can define methods on that module (or class) dynamically using define_method. For example:

module Version
  module_function

  HASH = { 
    major: 1,
    minor: 2,
    patch: 3,
  }

  HASH.each do |name, value|
    define_method(name) do
      return value
    end
  end
end

This will define a Version module with major, minor, and patch methods that return 1, 2, and 3, respectively.

Answer 5

you can extend the Hash class in the following way.

class Hash
      # return nil whenever the key doesn't exist
      def method_missing(m, *opts)
        if self.has_key?(m.to_s)
          return self[m.to_s]
        elsif self.has_key?(m.to_sym)
          return self[m.to_sym]
        end
        return nil

        # comment out above line and replace with line below if you want to return an error
        # super
      end
end