49 lines
1.5 KiB
Ruby
49 lines
1.5 KiB
Ruby
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# The Dependency Inversion Principle has to do with high-level (think business
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# logic) objects not depending on low-level (think database querying and IO)
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# implementation details. This can be achieved with duck typing and the
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# Dependency Inversion Principle. Often this pattern is used to achieve the
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# Open/Closed Principle that we discussed above. In fact, we can even reuse
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# that same example as a demonstration of this principle.
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# Now there is a formatter class, but I've hardcoded it on the Report class,
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# thus creating a dependency from the Report to the JSONFormatter. Since the
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# Report is a more abstract (high-level) concept than the JSONFormatter, we're
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# effectively breaking the DIP.
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class Report
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def body
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# Implementation
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end
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def print
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JSONFormatter.new.format(body)
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end
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end
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class JSONFormatter
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def format(body)
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# Implementation
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end
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end
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# Solution
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# This way the Report does not depend on the JSONFormatter and can use any type
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# of formatter that has a method called format (this is known as duck typing).
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# Another thing of note is that we've used, once again, dependency injection to
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# solve a problem. This technique is a very powerful one when our goal is
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# decoupling objects, and even though it has the same initials as the dependency
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# inversion principle (vs dependency injection pattern), they are completely
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# different concepts.
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class Report
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def body
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# Implementation
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end
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def print(formatter: JSONFormatter.new)
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formatter.format body
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end
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end
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