Strategy
Strategy
Known Uses
Both ET++ and InterViews use strategies to encapsulate different linebreaking algorithms as we've described.
In the RTL System for compiler code optimization, strategies define different register allocation schemes (RegisterAllocator) and instruction set scheduling policies (RISCscheduler, CISCscheduler). This provides flexibility in targeting the optimizer for different machine architectures.
The ET++SwapsManager calculation engine framework computes prices for different financial instruments. Its key abstractions are Instrument and YieldCurve. Different instruments are implemented as subclasses of Instrument. The YieldCurve calculates discount factors to present value of future cash flows. Both of these classes delegate some behavior to Strategy objects. The framework provides a family of ConcreteStrategy classes for generating cash flows, valuing swaps, and calculating discount factors. You can create new calculation engines by configuring Instrument and YieldCurve with the different ConcreteStrategy objects. This approach supports mixing and matching existing Strategy implementations as well as defining new ones.
The Booch components use strategies as template
arguments. The Booch collection classes support three different kinds of
memory allocation strategies: managed (allocation out of a pool),
controlled (allocations/deallocations are protected by locks), and
unmanaged (the normal memory allocator). These strategies are passed as
template arguments to a collection class when it's instantiated. For
example, an UnboundedCollection that uses the unmanaged strategy is
instantiated as UnboundedCollection
RApp is a system for integrated circuit layout. RApp must lay out and route wires that connect subsystems on the circuit. Routing algorithms in RApp are defined as subclasses of an abstract Router class. Router is a Strategy class.
Borland's ObjectWindows uses strategies in dialogs boxes to ensure that the user enters valid data. For example, numbers might have to be in a certain range, and a numeric entry field should accept only digits. Validating that a string is correct can require a table look-up.
ObjectWindows uses Validator objects to encapsulate validation strategies. Validators are examples of Strategy objects. Data entry fields delegate the validation strategy to an optional Validator object. The client attaches a validator to a field if validation is required (an example of an optional strategy). When the dialog is closed, the entry fields ask their validators to validate the data. The class library provides validators for common cases, such as a RangeValidator for numbers. New client-specific validation strategies can be defined easily by subclassing the Validator class.