Design Principles in Software Development

SOLID

Sources

• en.wikipedia.org/wiki/SOLID (opens new window)
• principles-wiki.net/collections:robert_c._martin_s_principle_collection (opens new window)

Single-responsibility principle (SRP)

There should never be more than one reason for a class to change." In other words, every class should have only one responsibility

Signs that will help you understand that the principle is violated:

• Unintentional duplication, when changes in one method affect another method result.
• A sign of a merger.

To understand and solve problems with it, think about actors / users of methods. We should split a code for different actors.

Bad example:

Employe
+ calculatePay + reportHours + save

To understand and solve problems with it, think about actors / users of methods. We should split a code for different actors.

Good example: Pattern "Facade".

Employe Facade
+ calculatePay + reportHours + save

↓ ↓ ↓

PayCalculator
+ calculatePay

HourReporter
+ reportHours

EmployeeSaver
+ saveEmployee

↓

Employee Data

Example in JavaScript:

//Bad

class UserSettings {
  constructor(user) {
    this.user = user;
  }

  changeSettings(settings) {
    if (this.verifyCredentials()) {
      // ...
    }
  }

  verifyCredentials() {
    // ...
  }
}

//Good

class UserAuth {
  constructor(user) {
    this.user = user;
  }

  verifyCredentials() {
    // ...
  }
}

Open / Closed Principle (OCP)

//

Liskov Substitution Principle (LSP)

//

Interface Segregation Principle (ISP)

//

Dependency Inversion Principle (DIP)

//