This post was inspired by the book Refactoring, which was written by Martin Fowler and Kent Beck.

Extract Function

The term "function" can be interchanged with "method" in an object-oriented language. The idea behinds it is that you look at a fragment of code, understand what it is doing, then extract it into its own function named after its purpose. With this principle, you can develop a habit of writing very small functions.

Take a look at the code below. We have a struct Rectangle and a method PrintInfo() to log the name and area of it.

package main

import "fmt"

type Rectangle struct {
    name   string
    width  int
    height int
}

func (s *Rectangle) PrintInfo() {
    fmt.Println("name:" + s.name)
    area := s.height * s.width
    fmt.Println("Area:" + fmt.Sprintf("%d", area))
}

func main() {
    rect := Rectangle{"Rect 1", 10, 5}
    rect.PrintInfo()
    // Name:Rect 1
    // Area:50
}

Applying the extract function rule here, we can extract calculation part area := s.height * s.width into a new method GetArea. Imagine you have a ton of calculations in PrintInfo(), the extract function will improve readability in your code.

package main

import "fmt"

type Rectangle struct {
    name   string
    width  int
    height int
}

func (s *Rectangle) PrintInfo() {
    fmt.Println("name:" + s.name)
    fmt.Println("Area:" + fmt.Sprintf("%d", s.GetArea()))
}

func (s *Rectangle) GetArea() int {
    return s.height * s.width
}

func main() {
    rect := Rectangle{"Rect 1", 10, 5}

    rect.PrintInfo()

    // Name:Rect 1
    // Area:50
}