229.md

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zntfdr

Design information flow

Truth vs. derived values:

• Where is truth?
• Who really knows that state which one place should be consulted for it?
• Values derived from truth are in many ways like a cache and needed to be treated as such

Define clear responsibilities

• Think of the inputs and outputs
• Separate out responsibilities from the rest of the program
• Use composition to build up larger pieces from smaller ones

Example: validators.

protocol Validator {
  validateWithError(error: NSErrorPointer) -> Bool
}

• Definition of “input” left open to interpretation

For example:

class SignUpValidator: Validator {
  let usernameValidator = UsernameValidator()
  let setPasswordValidator = SetPasswordValidator()
  let emailAddressValidator = EmailAddressValidator()
  ...
}

Simplify with immutability

Use Swift structs to avoid having objects changing data they're not supposed to change.