Implementation patterns

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Implementation Patterns

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Are read more often than written Most programs follow a small set of laws

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There is no such thing as "done" Most programs follow a small set of laws

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Structured using a basic set of state and control flow contepts Most programs follow a small set of laws

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Readers need to understand in detail and in concept Most programs follow a small set of laws

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Patterns are based on them Patterns help you write code Patterns work together

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How to structure iteration... Example ...the loop should be easy to read, easy to write, easy to modify and eficient.

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Values Principles Patterns

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Communication Values Code communicates well when the reader can understand it, modify it or use it Do you think of others when you program?

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Simplicity Values Eliminating excess complexity enables those reading, using and modifying programs to understand them more quickly Simplicity is in the eye of the beholder

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Flexibility Values Programs should be flexible, but only in ways they change Flexibility can come at the cost of increased complexity

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Values Principles Patterns

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Local Consequences Principles Structure the code so changes have local consecuences Keeping the cost of making changes low is a primary motivation

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Minimize Repetition Principles When you have the same code in several places, when you change one copy your change is no longer local Duplication is not evil, it just raises the cost of making changes

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Login and Data together Principles Put logic and the data it operates in the same method if possible, or in the same object or at least in the same package Logic and data are likely to have to change at the same time

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Simmetry Principles Simmetry is where the same idea is expressed the same way eveywhere it appers in the code Let's see an example!

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Simmetry Principles

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Declarative Expression Principles For those parts of a program that are more like simple facts, whithout sequence or conditionals, it is easier to read code that is simply declarative It requires that you follow the thread of execution

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Declarative Expression Principles

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Rate of Change Principles Put logic or data that changes at the same rate together and separate logic or data that changes at different rates These rates of change are a form of temporal simmetry

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Rate of Change Principles

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Values Principles Patterns

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Class State Behaviour Methods

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Class Classes are relatively expensive design. A class should do something significant.

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Class Reducing the number of clases in an system is an improvement... ...as long as the remaining classes do not become bloated.

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Class Simple Superclass Name Some of the most important names to choose well Names should be short and punchy, however sometimes you need several words Try to pick a strong metaphor: DrawingObject vs Figure

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Class Qualified Subclass Name The names of subclass have two jobs. They need to communicate what class they are like and thoy they are different. Prepend one or more modifiers to the superclass name to form a subclass name

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Class Abstract interface Every layer of interface has costs:It is one more thing to learn, understand, document, debug, organize, browse and name. Pay for interfaces only where you will need the flexibility they create. Maximizing the number of interfaces doesn't minimize the cost of software

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Class Interface Two styles of naming depend on how you are thinking of the interfaces: File - ActualFile, ConcreteFile, FileImpl (sufix and abbreviation!) IFile - File

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Class Abstract class They support change in the implementation and change of the interface. An interface says: "Here's how to access this kind of funcionality" A superclass says: "Here's one way to implement this functionality"

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Class Value object Draw the boundary between the world of state and the world of value