com.oracle.truffle.api.interop.java

Annotation Type MethodMessage

@Target(value=METHOD)
 @Retention(value=RUNTIME)
public @interface MethodMessage

Annotation to obtain fine grain control over behavior of JavaInterop.asJavaObject(java.lang.Class, com.oracle.truffle.api.interop.TruffleObject) wrapper interfaces. The interface created by JavaInterop.asJavaObject(java.lang.Class, com.oracle.truffle.api.interop.TruffleObject) method implements its methods by sending messsages to TruffleObject provided at the time of construction. There is a default sequence of operations for each method, which is good enough to read fields or invoke methods. However the Interop API is far richer and supports additional messages (not only the well known ones, but also arbitrary custom ones). To control which Message is sent one can annotate each method by this annotation.

Writing to a field

For example to write to field x of a JSON object:

 var obj = { 'x' : 5 }
 

one can define the appropriate wrapper interface as:

 interface ObjInterop {
   @MethodMessage(message = "WRITE")
   void x(int value);
 }
 

Then one can change the value of field x in obj from Java by calling:

 JavaInterop.asJavaObject(ObjInterop.class, obj).x(10);
 

the value of the x field is going to be 10 then.

Checking for Null

public static boolean isNullValue(TruffleObject obj) {
    return JavaInterop.isNull(obj);
}

Since:

0.9

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String	message Identification of the message to send.

Element Detail

message

public abstract String message

Identification of the message to send. Well known messages include fields of the Message class (e.g. "READ", "WRITE", "UNBOX", IS_NULL) or slightly mangled names of Message class factory methods ( EXECUTE, INVOKE). For more details on the string encoding of message names see Message.valueOf(java.lang.String) method.

Returns:

string identification of an inter-operability message

See Also:

Message.valueOf(java.lang.String)