As discussed above, object spaces form the basis of distributed objects by supplying the location. There are two main types of object space in SST: export sets and full object spaces.

Export sets, defined in SstSimpleObjectSpace, maintain lists of objects exported by a space. Export sets cannot manage remote references effectively.

Object spaces, defined in SstLocalSpace, maintain both an import and export set and can fully manage object identity and remote references. Importing an object makes a proxy to some remote object available locally.

The kind of space you require depends on your application. In general, if you are programming directly with invocation handlers such as an HTTP server, you will find export sets to be sufficient. Direct use of invocation handlers is ideal for pass-by-value applications. Systems requiring transient remote objects and object identity (pass-by-reference) should use full object spaces. The kind of space used is specified in the invocation handler configuration associated with your application's scheme. Again, the ping-pong examples contain samples of both approaches. Feel free to play with passing different values to see how the behavior varies. For example, try using a simple object such as aBoolean or anInteger for the with: part of the start:with: operation, and then try using an Array or some other complex object.