Basic programming principles

How to write a code

   |  Max Denissov

Using these principles allows you to write clear code.

Table of contents

  • Keep It Simple, Stupid (KISS)
  • Write DRY Code
  • Open/Closed
  • Composition Over Inheritance
  • Single Responsibility
  • Separation Of Concerns
  • You Aren’t Going To Need It (YAGNI)
  • Document Your Code
  • Refactor
  • Clean Code At All Costs

Keep It Simple, Stupid (KISS)

Unnecessary complexity should be avoided.

Source code:

fun sum(a: Int, b: Int): Int {
    val result = a + b
    return result
}

Problems:

  • Using an extra variable
  • Unnecessary lines of code

Refactored code:

fun sum(a: Int, b: Int): Int = a + b

Write DRY Code (Don’t Repeat Yourself)

Do not repeat data, do not repeat logic or DO NOT USE Copy-Paste.

Source code:

fun retrieveCountries(): List<Country> {
    httpClient.get<List<Country>>("https://server/api/countries") {
        header("Platform", "Android")
        header("Version", "1.0.0")
        header("Auth-Token", "")
    }
}

fun retrieveUsers(): List<User> {
    httpClient.get<List<User>>("https://server/api/users") {
        header("Platform", "Android")
        header("Version", "1.0.0")
        header("Auth-Token")
    }
}

Problems:

  • Repeating the same code lines
  • After editing a line in one place, you may forget to make changes in another
  • Reading unnecessary lines of code

Refactored code:


fun retrieveCountries(): List<Country> {
    httpClient.get<List<Country>>("https://server/api/countries") {
        addDefaultHeaders()
    }
}

fun retrieveUsers(): List<User> {
    httpClient.get<List<User>>("https://server/api/users") {
        addDefaultHeaders()
    }
}

// Extract logic in single place by making extensions, function and etc.
fun HttpRequestBuilder.addDefaultHeaders() {
    header("Platform", "Android")
    header("Version", "1.0.0")
    header("Auth-Token")
}

// Or use http client functionality like request interceptor, default request builder and etc.
val httpClient = HttpClient {
    install(DefaultRequest) {
        header("Platform", "Android")
        header("Version", "1.0.0")
        header("Auth-Token")
    }
}
programming principles  kotlin