com.oracle.truffle.api.library

Annotation Type GenerateLibrary.Abstract

@Retention(value=CLASS)
 @Target(value=METHOD)
public static @interface GenerateLibrary.Abstract

Makes a library message abstract, but allows to keep a default implementation. By default, abstract messages throw an AbstractMethodError if they are not exported for a given receiver type. To customize this behavior the library message can specify a method body and annotate it with GenerateLibrary.Abstract to keep requiring an implementation from exports.

For example:

 @GenerateLibrary
 public abstract class ArrayLibrary extends Library {

     @Abstract(ifExported = "read")
     public boolean isArray(Object receiver) {
         return false;
     }

     @Abstract(ifExported = "isArray")
     public int read(Object receiver, int index) {
         throw new UnsupportedOperationException();
     }
 }
 

In this example a receiver that does not export the ArrayLibrary will return false for isArray and throw an UnsupportedOperationException for read calls. A message may be made conditionally abstract by specifying the GenerateLibrary.Abstract.ifExported() attribute.

Since:

19.0

See Also:

GenerateLibrary.Abstract.ifExported()

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String[]	ifExported Specifies a message to be abstract only if another message is implemented.
String[]	ifExportedAsWarning Specifies a message to be abstract only if another message is implemented.

Element Detail

ifExported

public abstract String[] ifExported

Specifies a message to be abstract only if another message is implemented. Multiple other messages can be specified. If the list is empty, the message is always abstract unless GenerateLibrary.Abstract.ifExportedAsWarning() is not empty. If the list is not empty it takes precedence over GenerateLibrary.Abstract.ifExportedAsWarning().

For example:

 @GenerateLibrary
 public abstract class ArrayLibrary extends Library {

     @Abstract(ifExported = "read")
     public boolean isArray(Object receiver) {
         return false;
     }

     @Abstract(ifExported = "isArray")
     public int read(Object receiver, int index) {
         throw new UnsupportedOperationException();
     }
 }
 

In this example the isArray message only needs to be exported if the read message is exported and vice-versa.

Since:

19.0

Default:

{}

ifExportedAsWarning

public abstract String[] ifExportedAsWarning

Specifies a message to be abstract only if another message is implemented. Multiple other messages can be specified. The message is not actually made abstract unless it is in the GenerateLibrary.Abstract.ifExported() list. Only a warning is produced that prompts the user to implement the message

For example:

 @GenerateLibrary
 public abstract class MaybeNumberLibrary extends Library {

     public boolean isNumber(Object receiver) {
         return false;
     }

     @Abstract(ifExportedAsWarning = "isNumber")
     public Number getNumber(Object receiver) {
         throw new UnsupportedOperationException();
     }
 }
 

In this example, if the isNumber message is exported and the getNumber message is not, the user gets a warning.

Since:

23.0

Default:

{}