Golang cheatsheet for beginners

golang_cheatsheet.md

Golang cheatsheet

This cheatsheet was created by one of my colleague Austin. Just sharing it here because I found it useful

Install Go on your MAC

Follow these steps to install go onto your mac and test out the installation

Brief Intro

• fmt is the main package for printing stuff
  • fmt.Println(“something”)
  • fmt.Printf(“I have %d items”, 4)
• Initializing variables
  • var a string default to “”
  • var b int default to 0
  • var c bool default to false
  • a := “” will infer a is a string
  • b := 0 will infer b is an int
  • c := false will infer c is a bool
  • var d int
  • d = 5
  • Is the same as d := 5
• Case matters!!
  • Uppercase first letter means exporting variable, struct, function outside the package
  • Lowercase means variable, struct, function can only be used within package
• for is the only looping expressions
  • for {... somewhere a break} is a while loop with some condition to break out
  • for i := 0; i < N; i++ {...} is the standard for loop
  • for key, val := range myMap {...} iterates over each key in a map or in python a dict
  • for index, val := range mySlice {...} enumerates over a slice or in python a list
• Slices are like lists in the python
  • s := []int{1,2,3} creates a slice of int with 3 integers
  • s := make([]int, 5) initializes a slice of int set to 0 with a len and capacity of 5
  • s := make([]int, 0, 5) initializes a slice of int with len of 0 and capacity of 5
• Maps are like dicts in python
  • Must make before using
  • var b map[string]int results in b == nil and setting a key will result in a panic: assignment to entry in nil map
  • b := make(map[string]int) results in b != nilFunnnna
• Functions
  • func myFuncName(a, b int) int { return a+b }
  • In go everything is pass by value - Rob Pike
  • Treat structs, ints, float64, bool all as copied into a function
  • Maps and slices are passed in by their pointer so changing the values in the function changes the passed in map/slice
  • To retain the changes made to a struct, be sure to pass the struct’s address into the function instead of the struct itself
• Go routines
  • Very light weight ~ 4-8kb
  • Are scheduled onto threads
  • Could have thousands or millions of these running

import (
  “time”
  “fmt”
)

func main() {
  for i := 1; i < 4; i ++ {
    go func(sleepTime int) {
      time.Sleep(sleepTime *time.Seconds)
      fmt.Printf(“Finished sleeping %d seconds”, sleepTime)
    }(i)
  }
  time.Sleep(5 * time.Seconds)
}

• Sync waitgroup

  • Wait for a set number of go routines to complete
  • Add(n int) - set the number of go routines the wait group will wait to finish
  • Done() - lets a go routine signal it is done
  • Wait() - holds here for all go routines to finish

• Mutex

  • Allows you to lock a particular data structure, be it a struct or different levels of the struct

  type MyStruct {
    sync.Mutex
    Data []int
  }  

  • Lock()
  • Unlock()
  • b := MyStruct{}
  • b.Lock()
  • Do some stuff to the data field
  • b.Unlock()
  • Allows another go routine to modify the struct