Patterns for naming

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Patterns for naming
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Simple Superclass Name

• What should we call the root of a hierarchy?
• Complex name conveys full meaning.
• Simple name is easy to say, type, extend.
• But need to show that subclasses are related.

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Simple Superclass Name

• Give superclasses simple names two or
  (preferably) one word
• - Number
• - Collection
• - VisualComponent

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Qualified Subclass Name

• What should you call a subclass that plays a role
  similar to its superclass?
• Unique name conveys most information
• Derived name communicates relationship to
  superclass

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Qualified Subclass Name

• Use names with obvious meaning. Otherwise,
  prepend an adjective to most important
  superclass.
• - OrderedCollection
• - UndefinedObject
• - CloneFigureCommand, CompositeCommand,
  ConnectionCommand

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Variables Roles vs. Types

• Types are specified by classes
• aRectangle
• aCollection
• aView
• Roles - how an object is used
• location
• employees
• topView

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Role Suggesting Instance Variable

• What should you name an instance variable?
• Type is important for understanding
  implementation. But class comment can describe
  type.
• Role communicates intent, and this harder to
  understand than type.

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Role Suggesting Instance Variable

• Name instance variables for the role they play.
  Make the name plural if the variable is a
  collection.
• Point x, y
• Interval start, stop, step
• Polyline vertices

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Type Suggesting Parameter Name

• Name of variable can either communicate type or
  role.
• Keywords communicate their parameter's role, so
  name of variable should give new information.

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Type Suggesting Parameter Name

• Name parameters according to their most general
  expected class, preceded by "a" or "an". If
  there is more than one parameter with the same
  expected class, precede the class with a
  descriptive word.

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Temporaries

• Name temporaries after role they play.
• Use temporaries to
• collect intermediate results
• reuse result of an expression
• name result of an expression
• Methods are simpler when they don't use
  temporaries!

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Class Comments

• Every class should have a comment that describes
  the purpose of the class and the types of its
  instance variables

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Method comments

• Name of method should describe what it does.
• Name of arguments should describe what they are.
• Name of method should describe return type.
• Method comment should describe anything else that
  isnt obvious.

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Common State

• Different instances of a class have different
  values for some state. How do you represent it?
• Declare an instance variable in the class.
• Name the variable using Role Suggesting Instance
  Variable Name. Initialize it with either Lazy
  Initialization, Explicit Initialization, or a
  Constructor Parameter Method.

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Explicit Initialization

• How do you initialize instance variables to their
  default value?
• Make the code readable instead of changeable.
• Implement a method initialize that sets all the
  values. Override the class method new to
  invoke it on new instances.

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Lazy Initialization

• How do you initialize instance variables to their
  default value?
• Emphasize ease of change.
• Force all accesses to variable to go through
  accessing method. Make Getting method check
  whether the variable has been initialized and
  initialize it if necessary.

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Lazy Initialization

• Timercount
• count isNil
• ifTrue count self defaultCount
• count

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Default Value Method

• How do you represent the default value of a
  variable?
• Create a method that returns the value. Prepend
  default to the name of the variable as the name
  of the method.

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Constant Method

• How do you code a constant?
• Create a method that returns the constant.

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• How do you get and set an instance variables
  value?
• Direct Variable Access Access and set the
  variable directly.
• Indirect Variable Access Use a Getting Method
  and a Setting Method

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Collection Accessor Method

• How do you provide access to an instance variable
  that holds a collection?
• Provide methods that delegate to the collection.
  To name the methods, add the name of the
  collection to the collection name.
• addEmployee
• includesEmployee

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Enumeration Method

• How do you provide access to collection elements?
• Implement a method that executes a Block for each
  element of the collection. Name the method by
  concatenating the name of the collection and
  Do
• employeesDo

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Refactoring

• You dont always get your code right the first
  time.
• No - a first draft is never as good as a polished
  revision
• Bad names
• Long methods
• Direct access instead of indirect access

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Refactoring

• Why not just fix it?
• Causes errors
• Takes time
• If it isnt broken, dont fix it!
• Knowing how to refactor makes it faster and less
  error-prone
• Tools also help refactoring

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Refactoring

• Change in very small steps
• A refactoring shouldnt change behavior
• Run tests after each step.
• Write tests in SUnit and use TestRunner to run
  the tests.
• Write tests before refactoring!