Interfaces

Interfaces in ABS are similar to interfaces in Java. They have a name, which defines a nominal type, and they can extend one or more interfaces. If no explicit extends clause is given, the interface will extend the standard library interface ABS.StdLib.Object (see Object). The ABS.StdLib.Object interface does not specify any methods.

The interface body consists of a list of method signature declarations. Method names start with a lowercase letter.

Syntax

InterfaceDecl ::=	interface SimpleTypeIdentifier [ extends InterfaceList ]
	{ { MethSig } }
InterfaceList ::=	TypeIdentifier { , TypeIdentifier }
MethSig ::=	Type SimpleIdentifier
	( [ Type SimpleIdentifier { , Type SimpleIdentifier } ] ) ;

If a method declarations in an interface has an [Atomic] annotation, the compiler will statically check that any definitions for this method contain no suspension points (suspend and await statements), i.e., that running that method will complete without scheduling.

If a method declarations in an interface has a [Readonly] annotation, the compiler will statically check that any definitions for this method contain no assignments to fields.

Note

For ease of reasoning and analysis, ABS methods differ only by name. It is an error for an interface to declare two methods with the same name, either explicitly or via extending another interface.

The interfaces in the example below represent a database system, providing functionality to store and retrieve files, and a node of a peer-to-peer file sharing system. Each node of a peer-to-peer system plays both the role of a server and a client:

interface DB {
  File getFile(Filename fId);
  Int getLength(Filename fId);
  Unit storeFile(Filename fId, File file);
  Filenames listFiles();
}

interface Client {
  List<Pair<Server,Filenames>> availFiles(List<Server> sList);
  Unit reqFile(Server sId, Filename fId);
}

interface Server {
  Filenames inquire();
  Int getLength(Filename fId);
  Packet getPack(Filename fId, Int pNbr);
}

interface Peer extends Client, Server {
  List<Server> getNeighbors();
}