Question

Is it possible in Ruby to get a reference to methods of an object ( I would like to know if this can be done without procs/lambdas ) , for example , consider the following code :

 class X   def initialize     @map = {}     setup_map   end    private   def setup_map     # @map['a'] = get reference to a method     # @map['b'] = get reference to b method     # @map['c'] = get referebce to c method   end    public   def call(a)     @map['a'](a) if a > 10     @map['b'](a) if a > 20     @map['c'](a) if a > 30   end    def a(arg)      puts 'a was called with #{arg}'   end    def b(arg)      puts 'b was called with #{arg}'   end    def c(arg)     puts 'c was called with #{arg}'   end end 

Is it possible to do such thing ? I would like to avoid procs/lambdas because I want to be able to change the behaviour of A,B,C by subclassing .

Answer 1

You want Object#method:

---------------------------------------------------------- Object#method      obj.method(sym)    => method ------------------------------------------------------------------------      Looks up the named method as a receiver in obj, returning a Method       object (or raising NameError). The Method object acts as a closure       in obj's object instance, so instance variables and the value of       self remain available.          class Demo           def initialize(n)             @iv = n           end           def hello()             'Hello, @iv = #{@iv}'           end         end          k = Demo.new(99)         m = k.method(:hello)         m.call   #=> 'Hello, @iv = 99'          l = Demo.new('Fred')         m = l.method('hello')         m.call   #=> 'Hello, @iv = Fred' 

Now your code becomes:

private def setup_map   @map = {     'a' => method(:a),     'b' => method(:b),     'c' => method(:c)   }   # or, more succinctly   # @map = Hash.new { |_map,name| _map[name] = method(name.to_sym) } end  public def call(arg)   @map['a'][arg] if arg > 10   @map['b'][arg] if arg > 20   @map['c'][arg] if arg > 30 end