Notes and advantages of 'before/after' usage

Notes on the dispatching of before/after methods:

• A before (after) method is invoked just once per primary method invocation.

• The dispatching of before/after methods is thread-safe.

• The dispatching of before/after methods is fast. The time overhead for dispatching a primary method is on the order of N times the time to invoke a before/after method as a procedure, where N is the total number of before/after methods to be applied.

In conclusion, consider an example that clearly demonstrates the power of the composition of before/after metaclasses. Suppose you are creating a class library that will have n classes. Further suppose there are p properties that must be included in all combinations for all classes. Potentially, the library must have n2p classes. Let us hypothesize that (fortunately) all these properties can be captured by before/after metaclasses. In this case, the size of the library is n+p.

The user of such a library need only produce those combinations necessary for a given application. In addition, note that there is none of the usual programming. Given the IDL for a combination of before/after metaclasses, the SOM compiler generates the implementation of the combination (in either C or C++) with no further manual intervention.