Ruby 外观模式讲解和代码示例
外观是一种结构型设计模式， 能为复杂系统、 程序库或框架提供一个简单 （但有限） 的接口。
尽管外观模式降低了程序的整体复杂度， 但它同时也有助于将不需要的依赖移动到同一个位置。
复杂度：
流行度：
使用示例： 使用 Ruby 开发的程序中会经常使用外观模式。 它在与复杂程序库和 API 协作时特别有用。
识别方法： 外观可以通过使用简单接口， 但将绝大部分工作委派给其他类的类来识别。 通常情况下， 外观管理其所使用的对象的完整生命周期。
概念示例
本例说明了外观设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
main.rb: 概念示例
# The Facade class provides a simple interface to the complex logic of one or
# several subsystems. The Facade delegates the client requests to the
# appropriate objects within the subsystem. The Facade is also responsible for
# managing their lifecycle. All of this shields the client from the undesired
# complexity of the subsystem.
class Facade
# Depending on your application's needs, you can provide the Facade with
# existing subsystem objects or force the Facade to create them on its own.
def initialize(subsystem1, subsystem2)
@subsystem1 = subsystem1 || Subsystem1.new
@subsystem2 = subsystem2 || Subsystem2.new
end
# The Facade's methods are convenient shortcuts to the sophisticated
# functionality of the subsystems. However, clients get only to a fraction of
# a subsystem's capabilities.
def operation
results = []
results.append('Facade initializes subsystems:')
results.append(@subsystem1.operation1)
results.append(@subsystem2.operation1)
results.append('Facade orders subsystems to perform the action:')
results.append(@subsystem1.operation_n)
results.append(@subsystem2.operation_z)
results.join("\n")
end
end
# The Subsystem can accept requests either from the facade or client directly.
# In any case, to the Subsystem, the Facade is yet another client, and it's not
# a part of the Subsystem.
class Subsystem1
# @return [String]
def operation1
'Subsystem1: Ready!'
end
# ...
# @return [String]
def operation_n
'Subsystem1: Go!'
end
end
# Some facades can work with multiple subsystems at the same time.
class Subsystem2
# @return [String]
def operation1
'Subsystem2: Get ready!'
end
# ...
# @return [String]
def operation_z
'Subsystem2: Fire!'
end
end
# The client code works with complex subsystems through a simple interface
# provided by the Facade. When a facade manages the lifecycle of the subsystem,
# the client might not even know about the existence of the subsystem. This
# approach lets you keep the complexity under control.
def client_code(facade)
print facade.operation
end
# The client code may have some of the subsystem's objects already created. In
# this case, it might be worthwhile to initialize the Facade with these objects
# instead of letting the Facade create new instances.
subsystem1 = Subsystem1.new
subsystem2 = Subsystem2.new
facade = Facade.new(subsystem1, subsystem2)
client_code(facade)
output.txt: 执行结果
Facade initializes subsystems:
Subsystem1: Ready!
Subsystem2: Get ready!
Facade orders subsystems to perform the action:
Subsystem1: Go!
Subsystem2: Fire!
