In ruby there’s no method overloading. This is a problem when implementing
something like the Visitor pattern. One way to go around this is this one,
Instead of having visit(String s), we have visit_string(s).
When an object accepts the visitor, it uses it’s own class name to generate
the method it needs to call.
One big advantage of doing it like this, besides general DRYness, is that by
generating the method name dynamically, we can even distribute the
Visitable module and reuse it wherever. If we had done some sort of
non-dynamic case statement to dispatch, we’d have tied Visitable to a single
use case (for every new place we’d want to add it, we’d need to update this
case).
module Visitable
def accept(visitor)
method = "visit_#{self.class.name.downcase}"
visitor.send(method, self)
end
end
class Object; include Visitable; end
class Array
def accept(visitor)
visited = map { |element| element.accept(visitor) }
visitor.visit_array(self, visited)
end
end
class PrintVisitor
def visit_string(string)
"=#{string}="
end
def visit_fixnum(fixnum)
"!!#{fixnum}!!"
end
def visit_array(_, contents)
"<[#{contents.join(', ')}]>"
end
end
visitor = PrintVisitor.new
puts ["asf", 1, 2, "jl"].accept(visitor)