The XP language's type system

at 2010-10-10 in Language by friebe (0 comments)

As promised in the first article of our XP language series, we will have a look at the type system. The XP language knows about the following types:

Primitives - The following primitives exist: int, float, string and bool
Reference types - Classes, interfaces and enums, e.g. lang.Object, util.log.Traceable and util.DateInterval
Arrays - An array is a zero-based and continuously numbered list of any type, e.g. string[] or util.Date[].
Maps - A map is a hashtable mapping string keys to any type, e.g. [:string] or [:lang.XPClass]
The variable type - Marks a type that may either be a primitive or any reference type, declared with the keyword "var". The compiler will not be able to verify type correctness in this case and will warn about this - checks will be deferred until runtime.

Member variables, method parameters and return types need to be typed, while local variables don't - their type will be inferred on initialization.

Example

  public class Person {
    public string $name;                  // Member variable
    
    public void setName(string $name) {   // Method parameter
      $this.name= $name;
    }
    
    public string getName() {             // Return type
      return $this.name;
    }
    
    public string toString() {
      $s= $this.getClassName();           // Type inference, typeof($s) = string
      $s~= '(' ~ $this.name ~ ')';
      return $s;
    }
  }

As you can see, a method not returning any value is decorated with the void type, which may be used only in this place.

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The XP language's type system

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