Package com.oracle.truffle.api.dsl

Annotation Type TypeSystem

@Retention(CLASS)
@Target(TYPE)
public @interface TypeSystem

Each Node has one TypeSystem at its root to define the types that can be used throughout the system. Multiple TypeSystems are allowed, but they cannot be mixed inside a single Node hierarchy. A TypeSystem defines a list of types as its child elements, in which every type precedes its super types.The latter condition ensures that the most concrete type is found first when searching the list sequentially for the type of a given generic value.

Each value() is represented as a java type. A type can specify two annotations: TypeCheck and TypeCast. The TypeCheck checks whether a given generic value matches to the current type. The TypeCast casts a generic type value to the current type. If the TypeCheck and TypeCast annotations are not declared in the TypeSystem the a default implementation is provided. The default implementation of TypeCheck returns true only on an exact type match and TypeCast is only a cast to this type. Specified methods with TypeCheck and TypeCast may be used to extend the definition of a type in the language. In our example, the isInteger and asInteger methods are defined in a way so that they accept also Integer values, implicitly converting them to Double . This example points out how we express implicit type conversions.

Example: The TypeSystem contains the types Boolean, Integer, and Double. The type Object is always used implicitly as the generic type represent all values.

 @TypeSystem(types = {boolean.class, int.class, double.class})
 public abstract class ExampleTypeSystem {
 
     @TypeCheck
     public boolean isInteger(Object value) {
         return value instanceof Integer || value instanceof Double;
     }
 
     @TypeCast
     public double asInteger(Object value) {
         return ((Number)value).doubleValue();
     }
 }
 

See Also:

TypeCast, TypeCheck

Required Element Summary

Required Elements

Modifier and Type	Required Element	Description
java.lang.Class<?>[]	value	The list of types as child elements of the TypeSystem.

Element Detail

value

java.lang.Class<?>[] value

The list of types as child elements of the TypeSystem. Each precedes its super type.