If this code is not a joke, how on earth does it work?

问题

class Tree
  def initialize*d;@d,=d;end
  def to_s;@l||@r?",>":@d;end
  def total;(@d.is_a?(Numeric)?@d:0)+(@l?@l.total: 0)+(@r?@r.total: 0);end
  def insert d
    alias g instance_variable_get
    p=lambda{|s,o|d.to_s.send(o,@d.to_s)&&
      (g(s).nil??instance_variable_set(s,Tree.new(d)):g(s).insert(d))}
    @d?p[:@l,:]:@d=d
  end
end

Would anyone like to take a stab at explaining what this does? It appeared as an answer in a question I asked about code that is too clever. But it's too clever for me to tell whether it's simply a joke. If it's not, I'd be interested to know how it works, should anyone care to explain.

回答1:

EDIT: The person who posted the original obfuscated example gave the actual source code in his answer. He also posted a corrected version of the obfuscated code, because as I noted, some of it didn't make sense even when you removed the funky syntax.

That is some nicely obfuscated code. As with most obfuscated code, it's mostly a lot of ternary operators and a stubborn refusal to put in whitespace where a normal person would. Here is basically the same thing written more normally:

class Tree
  def initialize(*d)
    @d,  = d # the comma is for multiple return values,
             # but since there's nothing after it,
             # all but the first are discarded.
  end
  def to_s
    @l || @r ? ",>" : @d
  end
  def total
    total = @d.is_a?(Numeric) ? @d : 0
    total += @l.total if @l
    total += @r.total if @r
  end
  def insert(arg)
    if @d
      if @l
        @l.insert(arg)
      else
        @l = Tree.new(arg)
      end
    else
      @d = arg
    end
  end
end

The insert method is not syntactically valid (it's missing a method name at one part), but that's essentially what it does as far as I can tell. The obfuscation in that method is pretty thick:

Instead of just doing @l = whatever, it uses instance_variable_get() and instance_variable_set(). Even worse, it aliases instance_variable_get() to just be g().
It wraps most of the functionality in a lambda function, to which it passes the name of the @l. Then it calls this function with the lesser-known syntax of func[arg1, arg2], which is equivalent to func.call(arg1, arg2).

回答2:

This appears to be a binary tree implementation in very few lines. I apologize if my understanding of the ruby syntax is limited:

class Tree                    // defining the class Tree

    def initialize *d;        // defines the initializer
        @d = d;               // sets the node value
    end

    def to_s;                 // defines the to_s(tring) function
        @l || @r ? ",>" : @d; // conditional operator. Can't tell exactly what this 
                              // function is intending. Would think it should make a
                              // recursive call or two if it's trying to do to_string
    end

    def total;                // defines the total (summation of all nodes) function
        @d.is_a ? (Numeric)   // conditional operator.  Returns
            ? @d              // @d if the data is numeric
            : 0               // or zero
        + (@l ? @l.total : 0) // plus the total for the left branch
        + (@r ? @r.total : 0) // plus the total for the right branch
    end

    def insert d              // defines an insert function
        ??                    // but I'm not going to try to parse it...yuck
    end

Hope that helps some... :/

回答3:

It started off as this:

class Tree
  include Comparable

  attr_reader :data

  # Create a new node with one initial data element
  def initialize(data=nil)
    @data = data
  end

  # Spaceship operator. Comparable uses this to generate
  #   <, <=, ==, =>, >, and between?
  def <=>(other)
    @data.to_s <=> other.data.to_s
  end

  # Insert an object into the subtree including and under this Node.
  # First choose whether to insert into the left or right subtree,
  # then either create a new node or insert into the existing node at
  # the head of that subtree.
  def insert(data)
    if !@data
      @data = data
    else
      node = (data.to_s < @data.to_s) ? :@left : :@right
      create_or_insert_node(node, data)
    end
  end

  # Sum all the numerical values in this tree. If this data object is a
  # descendant of Numeric, add @data to the sum, then descend into both subtrees.
  def total
    sum = 0
    sum += @data if (@data.is_a? Numeric)
    sum += [@left, @right].map{|e| e.total rescue 0}.inject(0){|a,v|a+v}
    sum
  end

  # Convert this subtree to a String.
  # Format is: <tt>\<data,left_subtree,right_subtree></tt>.
  # Non-existant Nodes are printed as <tt>\<></tt>.
  def to_s
    subtree = lambda do |tree|
      tree.to_s.empty? ? "<>" : tree
    end
    "<#{@data},#{subtree[@left]},#{subtree[@right]}>"
  end

  private ############################################################
  # Given a variable-as-symbol, insert data into the subtree incl. and under this node.
  def create_or_insert_node(nodename, data)
    if instance_variable_get(nodename).nil?
      instance_variable_set(nodename, Tree.new(data))
    else
      instance_variable_get(nodename).insert(data)
    end
  end

end

I think I actually broke it when I was shortening it down. The nine-line version doesn't quite work. I had fun regardless. :P

This was my favourite part:

def initialize*d;@d,=d;end

This is acutally making use of parallel assignment to save a couple characters. You could expand this line to:

def initialize(*d)
  @d = d[0]
end

回答4:

I posted the original code. Sorry, but I didn't bother to check that I even did it right, and a bunch of stuff got stripped out because of less than signs.

class Tree
  def initialize*d;@d,=d;end
  def to_s;@l||@r?"<#{@d},<#{@l}>,<#{@r}>>":@d;end
  def total;(@d.is_a?(Numeric)?@d:0)+(@l?@l.total: 0)+(@r?@r.total: 0);end
  def insert d
    alias g instance_variable_get
    p=lambda{|s,o|d.to_s.send(o,@d.to_s)&&
      (g(s).nil??instance_variable_set(s,Tree.new(d)):g(s).insert(d))}
    @d?p[:@l,:<]||p[:@r,:>]:@d=d
  end
end

That's what it should look like.

来源：https://stackoverflow.com/questions/715951/if-this-code-is-not-a-joke-how-on-earth-does-it-work

标签

ruby

obfuscation