Of course it takes some heuristic to jump to the definition of these common Rails idioms

  belongs_to :customer # class Customer
  after_save :do_something # method
  validate :custom_validation # method

or a Ruby send(:method, arg)

But an IDE specialized in Ruby can do it. No idea if RubyMine does it.

Bonus for handling

  send("method_#{var}".to_sym, arg)

In general it can only present a menu of choices: all the methods with a name starting with "method_"