CoreLinux++ Functional Requirement Document
Revision $Revision: 1.2 $
Last Modified : Tuesday, February 1, 2000

Title : Flyweight Pattern

Requirement ID: 3146
Analysis References: Use Case Report, Analysis Diagrams
Design References: Class Report, Design Diagrams
Cross References: AbstractFactory

1. Introduction

Flyweights model concepts or entities that are normally too plentiful to represent with objects. Often times a system is built without realizing the scaleability and performance issues with a proliferation of fine grained object instances.

A Flyweight is a shared object that can be used in multiple contexts simultaneously, acting as a independent object in each context, it is indistinguishable from an instance of the object that's not shared.

1.1 Deliverables Overview

The participants in the Flyweight pattern include:

Flyweight

Declares an interface through which flyweights can receive and act on extrinsic states.

ConcreteFlyweight

Implements the Flyweight interface and adds storage for intrinsic state. A ConcreteFlyweight object must be shareable. Any state it stores must be intrinsic; that is, it must be independent of the ConcreteFlyweight object's context.

UnsharedConcreteFlyweight

Not all Flyweight subclasses need to be shared. The Flyweight interface enables sharing; it doesn't enforce it.

FlyweightFactory

Creates and manages flyweight objects. Ensures that flyweights are shared properly. When a client requests a flyweight, the FlyweightFactory object supplies an existing instance or creates one, if none exists.

The deliverable is mostly vacuous, with the exception of the FlyweightFactory, in that we want to capture the participants abstractions.

The CoreLinux++ team will deliver Flyweight implementations for specific cases as needed.

Users can utilize the participant abstractions as a basis for creating their own Flyweight implementation outside of the libcorelinux++ library.

2. Functional Requirements

Flyweight and participants will be publicly available for extension.

2.1 User Interface Specifications

NA

2.2 Product Services

NA

2.3 External Interfaces and Database Requirements

NA

2.4 Error Handling

NA

2.5 Foreseeable Functional Changes and Enhancements

NA.

3. Non-Functional Requirements

Precondition constraints: None

Postcondition constraints: None

Invarient constraints: None

3.1 Performance Requirements

NA

3.2 User Documentation and Other User Aids

This Document

Analysis Use-Case diagrams

Design class diagrams

3.3 Development Requirements

Standards: CoreLinux++ C++ Standards and Guidelines

Will be part of the libcorelinux++ shared library.

3.4 Foreseeable Non-Functional Changes

NA

4. Remarks and Guidelines for Later Life Cycle Phases

TBD

5. Term Glossary

TBD