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Adapter

Метки: python

When you’ve got this, and you need that, Adapter solves the problem. The only requirement is to produce a that, and there are a number of ways you can accomplish this adaptation:

# ChangeInterface/Adapter.py
# Variations on the Adapter pattern.

class WhatIHave:
    def g(self): pass
    def h(self): pass

class WhatIWant:
    def f(self): pass

class ProxyAdapter(WhatIWant):
    def __init__(self, whatIHave):
        self.whatIHave = whatIHave

    def f(self):
        # Implement behavior using
        # methods in WhatIHave:
        self.whatIHave.g()
        self.whatIHave.h()

class WhatIUse:
    def op(self, whatIWant):
        whatIWant.f()

# Approach 2: build adapter use into op():
class WhatIUse2(WhatIUse):
    def op(self, whatIHave):
        ProxyAdapter(whatIHave).f()

# Approach 3: build adapter into WhatIHave:
class WhatIHave2(WhatIHave, WhatIWant):
    def f(self):
        self.g()
        self.h()

# Approach 4: use an inner class:
class WhatIHave3(WhatIHave):
    class InnerAdapter(WhatIWant):
        def __init__(self, outer):
            self.outer = outer
        def f(self):
            self.outer.g()
            self.outer.h()

    def whatIWant(self):
        return WhatIHave3.InnerAdapter(self)

whatIUse = WhatIUse()
whatIHave = WhatIHave()
adapt= ProxyAdapter(whatIHave)
whatIUse2 = WhatIUse2()
whatIHave2 = WhatIHave2()
whatIHave3 = WhatIHave3()
whatIUse.op(adapt)
# Approach 2:
whatIUse2.op(whatIHave)
# Approach 3:
whatIUse.op(whatIHave2)
# Approach 4:
whatIUse.op(whatIHave3.whatIWant())

I’m taking liberties with the term “proxy” here, because in Design Patterns they assert that a proxy must have an identical interface with the object that it is a surrogate for. However, if you have the two words together: “proxy adapter,” it is perhaps more reasonable.