Wednesday, 29 February 2012

Typed Integers

I really like the idea of typed integers. For example, if you a number representing the number of cats and a number representing a number of dogs it is possible to add these together.  In a typed integer world it would not be possible and throw an error upon compilation.  I think this would be a big improvement for API safety and also a method of documentation.  There is nothing worse than a method with a structure like #foo(int, int) which is difficult to understand without reading or documentation every time.

In general use this would be suicide in a managed language where the overhead of an object for every int could mean a huge jump in memory usage and GC wouldn't be worth the improvements.  The actual implementation in Java would also be extremely ugly, for example:

class EventID {
  private final int id;
  public EventID(int anID) {
    id = anID;

The class doesn't even contain basic methods like a way to get the ID, compare or hash it which with an int you get for free and it is still a fair wedge of code.  Lombok's @Data annotation can really improve classes like this and make the language feel more declarative.

I have found the best language to implement this is c++, the following is my proof of concept implementation:

class TypedInt
  const int value;

  TypedInt(int v) : value(v) {};

  TypedInt operator + (TypedInt num)
    TypedInt result(value + num.value);

    return result;

  TypedInt  operator = (const int other)
    TypedInt result(other);

    return result;

This allows the following usage:

struct eventid {};

typedef TypedInt EventId;
EventId i = 2, j = 3;

EventId result = i + j;

Overall this feels natural to use.  If I was actually using class then the other operators such as == could be implemented without problems. 

One of the benefits of c++ is that an object wrapping an int does not take more memory than an int would, during compilation this abstraction is apparently stripped away.

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