"Clean Architecture: A Craftsman's Guide to Software Structure and Design" 1 - Introduction and Programming Paradigms
This post is a note for Part I (Introduction), and Part II (Programming Paradigms) in Clean Architecture: A Craftsman’s Guide to Software Structure and Design by Robert C. Matrin.
1. What is Design and Architecture?
- NO DIFFERENCES BETWEEN THEM
- Usually “architecture” means structure at a high-level, and “design” means structure at a low-level. But Low-level details (design) and the high-level structure (architecture) are all part of the software design.
- The goal of software architecture is to minimize the human resources required to build and maintain the required system.
- Design quality can be measured by the effort. If required effort is high, the design is bad.
- The best option in every case is to recognize and avoid its overconfident and to start taking the quality of software architecture seriously.
2. A Tale of Two Values.
- Two values: behavior, structure
- The first value of software -behavior- is urgent but not always particularly important.
- The second value of software -architecture- is important but never particularly urgent.
- Both things should be remained high, but we can arrange works into these four priorities.
- Urgent and important
- Not urgent and important
- Urgent and not important
- Not urgent and not important
- Note that the architecture of the code is in the top two positions.
- The responsibility of software developers is to assert the importance of architecture over the urgency of features.
Starting With The Bricks: Programming Paradigms
- Paradigms: the ways of programming, relatively unrelated to languages.
- A paradigm tells you which programming structures to use, and when to use them.
3. Paradigm Overview
- three paradaigms: Structured Programming, Object-Orient Programming, and Functional Programming.
- Note: Each of the paradigms removes capabilities from the programmer. None of them adds new capabilities.
4. Structured Programming
- Why was Structured Programming born? All programs can be built with a minimum set of control structures. (sequence, selection, and iteration)
- Structured Programming allows modules to be recursively decomposed into provable units, so we can decompose a large-scale problem into high-level functions. And each of those functions can be decomposed into lower-level functions.
“Testing shows the presence, not the absence, of bugs” by Dijkstra.
5. Object-Oridented Programming
- Three magic words for Object-Oriented: encapsulation, inheritance, and polymorphism
- Encapsulation makes data to be hidden and required function to be shown.
- Inheritance is simply the redeclaration of a group of variables and functions within an enclosing scope.
- Encapsulation does not make OO great itself, and perhaps inheritance can make OO better.
- Polymorphism helps OO to allow the plugin architecture to be used anywhere.
- In traditional software architecture, source code dependencies should follow the flow of control.
- But OO languages provide safe and convenient polymorphism, so source code dependencies can be inverted. (Dependency Inversion)
- OO is the ability, through the use of polymorphism, to gain absolute control over every source code dependency in the system.
6. Functional Programming
- Other programming languages are using a mutable variable as a loop control variable, but in functional languages no such mutable variable exists.
- Because all race conditions, deadlock conditions, and concurrent issues are due to mutable variables.
- Segregation of Mutability
- One of the most common compromises in regard to immutability is to segregate the application into mutable and immutable components.
- Architects would be wise to push as much processing as possible into the immutable components.
- Event Sourcing
- Event sourcing is a strategy wherein we store the transactions, but not the state. (In bank applications, imagine that storing transactions instead of balance.)
- Then, nothing ever gets deleted or updated from such a data store. As a consequence, our applications are not CRUD; they are just CR.
- If we have enough storage and process power, we can make our applications entirely immutable and functional.