IT wisdom

Good software [Beck]:

1. Passes the tests
2. Reveals intention
   • I will contend that Conceptual Integrity is the most important consideration in system design. It is better to have a system omit certain anomalous features and improvements, but to reflect one set of design ideas, than to have one that contains many good but independent and uncoordinated ideas. [Brooks]
   • Simplicity and clarity —in short: what mathematicians call "elegance"— are not a dispensable luxury, but a crucial matter that decides between success and failure [Dijkstra]
   • Convention over configuration
   • Separation of Concerns
   • Maximum coherence, minimum dependency
3. No duplication
   • Don’t Repeat Yourself (DRY)
   • Single Point of Truth (SPOT)
4. Fewest elements
   • A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. [Antoine de Saint-Exupéry]
   • Less is More
   • Occam's razor: the simplest option is usually correct
   • Keep It Small and Simple (KISS) until proven complex
   • Make everything as simple as possible, but not simpler [Einstein]
   • Measuring programming progress by lines of code is like measuring aircraft building progress by weight. [Gates]

Snippets:

• From the Gang of Four:
  • Program to an interface, not an implementation
  • Favor object composition over class inheritance
• Algemene namen:
  • Foo, bar
  • Alice, Bob, Carol & Dave
• Make the change easy. Then make the easy change.
• Technology develops from the primitive via the complex to the simple. [Antoine de Saint-Exupéry]
• Command Query Separation: Functions that change state should not return values and functions that return values should not change state.
• Death by Arguments
• Refactoring Catalog
• Principles of OOD:
  • Class design:
    • SRP (Single Responsibility Principle): A class should have one, and only one, reason to change.
    • OCP (Open Closed Principle): You should be able to extend a classes behavior, without modifying it.
    • LSP (Liskov Substitution Principle): Derived classes must be substitutable for their base classes.
    • ISP (Interface Segregation Principle): Make fine grained interfaces that are client specific.
    • DIP (Dependency Inversion Principle): Depend on abstractions, not on concretions.
  • Package¹ cohesion (what to put inside packages):
    • REP (Release Reuse Equivalency Principle): The granule of reuse is the granule of release.
    • CCP (Common Closure Principle): Classes that change together are packaged together.
    • CRP (Common Reuse Principle): Classes that are used together are packaged together.
  • package couplings (metrics that evaluate the package structure of a system):
    • ADP (Acyclic Dependencies Principle): The dependency graph of packages must have no cycles.
    • SDP (Stable Dependencies Principle): Depend in the direction of stability.
    • SAP (Stable Abstractions Principle): Abstractness increases with stability.

About IT:

• IT connects people and systems
• IT is a craft
• IT is human labour

Snippets:

• Deploy Early and Often (DEO) / Release Early, Release Often (RERO)
• Problem vs Work
• Realistische ambitie
• Pareto principle: 20/80% rule
• Lacking quality, rules abound.