Duck typing alows true polymorfisim

ruby-talk
1

In comp.lang.java.advocacy, atbusbook@aol.com
<atbusbook@aol.com>

lets say you want a generic numerical algorithom like sum

Ruby

def sum lst
  lst.inject(0){|total,current| total*current}
end

Java // i dont know if there is a numeric super class for numbers

class Sum{
  public static int sum(int lst){
    int total = 0;
    for(int current : lst){
      total+=current;
    }
    return total;
  }
  // repeat for all other number types
}

There isn't; Java makes the distinction between an int and
an Integer, a double and a Double. Java 5 did introduce
autoboxing, which makes things like

Number numbers = new Number{1, 2.3, 4, 5.6};

possible, and Number is a baseclass for both Integer and
Double (but not int and double).

Therefore, one could write:

public class Sum {
  public static double sum(int lst)
  {
    Number nlst = new Number[lst.length];
    for(int i = 0; i < nlst.length; i++) nlst[i] = new Integer(lst[i]);
    return sum(Arrays.asList(nlst));
  }
  public static double sum(double lst)
  {
    Number nlst = new Number[lst.length];
    for(int i = 0; i < nlst.length; i++) nlst[i] = new Double(lst[i]);
    return sum(Arrays.asList(nlst));
  }
  public static double sum(float lst)
  {
    Number nlst = new Number[lst.length];
    for(int i = 0; i < nlst.length; i++) nlst[i] = new Double(lst[i]);
    return sum(Arrays.asList(nlst));
  }
  public static double sum(Number lst)
  {
    return sum(Arrays.asList(lst));
  }
  public static double sum(Collection<Number> lst)
  {
    double sum = 0;
    for(Iterator<Number> i = lst.iterator(); i.hasNext())
      sum += i.next().doubleValue();
    return sum;
  }

}

A rather ugly but possibly useful duckling.

···

wrote on 25 Aug 2006 12:05:21 -0700 <1156532721.879808.40990@i3g2000cwc.googlegroups.com>:

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