Go Cheat Sheet

Learn Go from the basics →

Variables & Types

var age int = 36: Declare with an explicit type
name := "Ada": Short declaration with type inference (inside functions)
const Pi = 3.14159: Constant
n, err := strconv.Atoi("42"): Convert a string to an int
float64(x): Explicit type conversion

Control Flow

if v, ok := m["k"]; ok { }: if with an init statement
for i := 0; i < 10; i++ { }: Counting loop
for i, v := range items { }: Iterate a slice with index and value
for cond { }: While-style loop
switch day { case "Sat", "Sun": ... default: ... }: Switch (no implicit fallthrough)

Slices & Maps

nums := []int{1, 2, 3}: Slice literal
nums = append(nums, 4): Append (always reassign the result)
nums[1:3]: Sub-slice (shares the backing array)
ages := map[string]int{"ada": 36}: Map literal
v, ok := ages["bob"]: Comma-ok lookup
delete(ages, "ada"): Remove a key

Functions & Errors

func div(a, b float64) (float64, error) { }: Multiple return values
if err != nil { return err }: Check and propagate an error
fmt.Errorf("load config: %w", err): Wrap an error with context
errors.Is(err, os.ErrNotExist): Check for a wrapped error
defer f.Close(): Run when the function returns

Structs, Methods & Interfaces

type User struct { Name string; Age int }: Struct type
func (u *User) Birthday() { u.Age++ }: Method with a pointer receiver
type Shape interface { Area() float64 }: Interface (satisfied implicitly)
s, ok := v.(Circle): Type assertion
func Max[T cmp.Ordered](a, b T) T { }: Generic function

Concurrency

go work(): Start a goroutine
ch := make(chan int, 10): Buffered channel
ch <- v / v := <-ch: Send / receive
select { case v := <-ch: ... case <-time.After(time.Second): ... }: Wait on several channel operations
var wg sync.WaitGroup; wg.Add(1); defer wg.Done(); wg.Wait(): Wait for goroutines to finish

Tooling

go mod init example.com/app: Start a new module
go run .: Compile and run
go build -o app: Build a native binary
go test ./... -race -cover: Run all tests with the race detector
gofmt -w . / go vet ./...: Format and statically check code