# Here are three ways of running a proc with "local variables" set.
# Really they aren't local variables but functions, it seems it is
# impossible to set local variables or run procs with bindings which
# have the variables set. Trust me I've tried.


# METHOD 1: WITH A CLASS
# ----------------------
# Create a class then set methods for each arg, then run the proc in
# the newly created class.
#
def in_class(args, proc)
  k = Class.new

  args.each do |a,v|
    k.send(:define_method, a) { v }
  end

  k.new.instance_exec &proc
end

# METHOD 2: USING METHOD MISSING
# ------------------------------
# Only create one class, which is then stored in a @var, this then
# takes the arguments and uses method missing to pass the correct
# value from the hash.
#
def in_missing_class(a, f)
  if @k
    if f.arity > 0
      @k.new(a).instance_exec(a, &f)
    else
      @k.new(a).instance_exec(&f)
    end
  else
    @k = Class.new {
      def initialize(args)
        @a = args
      end

      def method_missing(sym, *args)
        if @a.has_key?(sym)
          @a[sym]
        else
          super
        end
      end
    }
    in_missing_class(a, f)
  end
end

# METHOD 3: USING METHOD MISSING AGAIN
# ------------------------------------
# This time create a single instance of a class which has a method
# allowing you to set the hash of args each time it is called, this
# way you aren't creating lots of different instances of a class.
#
def in_missing_object(a, f)
  if @o
    @o._run a, f
  else
    @o = Class.new {
      def _run(a, f)
        @a = a
        if f.arity > 0
          instance_exec(a, &f)
        else
          instance_exec &f
        end
      end

      def method_missing(sym, *args)
        if @a.has_key?(sym)
          @a[sym]
        else
          super
        end
      end
    }.new
  end
end

a = {:name => "world"}
f = proc { puts "Hello, #{name}!" }

in_class(a, f)
#=> Hello, world!
in_missing_class(a, f)
#=> Hello, world!
in_missing_object(a, f)
#=> Hello, world!