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package com.oracle.truffle.api.library;
import com.oracle.truffle.api.library.GenerateLibrary.Abstract;
A library that allows to dynamically dispatch to export library classes. Sometimes the target exports for a receiver type cannot be statically determined by the receiver class with the ExportLibrary annotation. To allow such types to dynamically dispatch to exports the dynamic dispatch library can be exported instead. By exporting dynamic dispatch the export target can be chosen dynamically.
The dynamic dispatch library requires to implement the dispatch method. The dispatch method
returns the target exports class that this receiver should dispatch to. If it returns
null then the type will dispatch to the library default exports. The implementation of the dispatch must be stable for a single receiver value. For example it is not allowed to change the dispatch target for a receiver instance. If the dispatch target was changed while the receiver was used by a library then an AssertionError will be thrown.
Full usage example
@ExportLibrary(DynamicDispatchLibrary.class)
static final class DispatchObject {
final Object data;
final Class dispatchTarget;
DispatchObject(Object data, Class dispatchTarget) {
this.data = data;
this.dispatchTarget = dispatchTarget;
}
@ExportMessage
Class dispatch() {
return dispatchTarget;
}
}
@GenerateLibrary
public abstract static class ArrayLibrary extends Library {
public boolean isArray(Object receiver) {
return false;
}
public abstract int read(Object receiver, int index);
}
@ExportLibrary(value = ArrayLibrary.class, receiverType = DispatchObject.class)
static final class DispatchedBufferArray {
@ExportMessage
static boolean isArray(DispatchObject o) {
return true;
}
@ExportMessage
static int read(DispatchObject o, int index) {
return ((int[]) o.data)[index];
}
}
public static void main(String[] args) {
ArrayLibrary arrays = LibraryFactory.resolve(ArrayLibrary.class).getUncached();
assert 42 == arrays.read(new DispatchObject(new int[]{42}, DispatchedBufferArray.class), 0);
}
Since: 19.0
/**
* A library that allows to dynamically dispatch to export library classes. Sometimes the target
* exports for a receiver type cannot be statically determined by the receiver class with the
* {@link ExportLibrary} annotation. To allow such types to dynamically dispatch to exports the
* dynamic dispatch library can be exported instead. By exporting dynamic dispatch the export target
* can be chosen dynamically.
* <p>
* The dynamic dispatch library requires to implement the dispatch method. The dispatch method
* returns the target exports class that this receiver should dispatch to. If it returns
* <code>null</code> then the type will dispatch to the library default exports. The implementation
* of the dispatch must be stable for a single receiver value. For example it is not allowed to
* change the dispatch target for a receiver instance. If the dispatch target was changed while the
* receiver was used by a library then an {@link AssertionError} will be thrown.
* <p>
* <h4>Full usage example</h4>
*
* <pre>
* @ExportLibrary(DynamicDispatchLibrary.class)
* static final class DispatchObject {
*
* final Object data;
* final Class<?> dispatchTarget;
*
* DispatchObject(Object data, Class<?> dispatchTarget) {
* this.data = data;
* this.dispatchTarget = dispatchTarget;
* }
*
* @ExportMessage
* Class<?> dispatch() {
* return dispatchTarget;
* }
* }
*
* @GenerateLibrary
* public abstract static class ArrayLibrary extends Library {
*
* public boolean isArray(Object receiver) {
* return false;
* }
*
* public abstract int read(Object receiver, int index);
* }
*
* @ExportLibrary(value = ArrayLibrary.class, receiverType = DispatchObject.class)
* static final class DispatchedBufferArray {
*
* @ExportMessage
* static boolean isArray(DispatchObject o) {
* return true;
* }
*
* @ExportMessage
* static int read(DispatchObject o, int index) {
* return ((int[]) o.data)[index];
* }
* }
*
* public static void main(String[] args) {
* ArrayLibrary arrays = LibraryFactory.resolve(ArrayLibrary.class).getUncached();
* assert 42 == arrays.read(new DispatchObject(new int[]{42}, DispatchedBufferArray.class), 0);
* }
* </pre>
*
* @since 19.0
*/
@GenerateLibrary(dynamicDispatchEnabled = false)
public abstract class DynamicDispatchLibrary extends Library {
Constructor for generated subclasses. Subclasses of this class are generated, do not extend
this class directly.
Since: 19.0
/**
* Constructor for generated subclasses. Subclasses of this class are generated, do not extend
* this class directly.
*
* @since 19.0
*/
protected DynamicDispatchLibrary() {
}
Returns a class that exports at least one library with an explicit receiver. Returns null to indicate that the default dispatch of the library
should be used.
Since: 19.0
/**
* Returns a class that {@link ExportLibrary exports} at least one library with an explicit
* receiver. Returns <code>null</code> to indicate that the default dispatch of the library
* should be used.
*
* @since 19.0
*/
@Abstract
public Class<?> dispatch(@SuppressWarnings("unused") Object receiver) {
return null;
}
Cast the object receiver type to the dispatched type. This is not supposed to be implemented
by dynamic dispatch implementer but is automatically implemented when implementing dynamic
dispatch.
Since: 19.0
/**
* Cast the object receiver type to the dispatched type. This is not supposed to be implemented
* by dynamic dispatch implementer but is automatically implemented when implementing dynamic
* dispatch.
*
* @since 19.0
*/
/*
* Implementation Note: This message is known by the annotation processor directly. No need to
* export it as a library message. It is also not allowed to be implemented directly by the
* dynamic dispatch implementer.
*/
public abstract Object cast(Object receiver);
static final LibraryFactory<DynamicDispatchLibrary> FACTORY = LibraryFactory.resolve(DynamicDispatchLibrary.class);
Returns the library factory for DynamicDispatchLibrary. Since: 19.0
/**
* Returns the library factory for {@link DynamicDispatchLibrary}.
*
* @since 19.0
*/
public static LibraryFactory<DynamicDispatchLibrary> getFactory() {
return FACTORY;
}
}