1 Golang CheatSheet

PDF Link: cheatsheet-golang-A4.pdf, Category: languages
Blog URL: https://cheatsheet.dennyzhang.com/cheatsheet-golang-A4
Related posts: Ruby CheatSheet, Python CheatSheet, #denny-cheatsheets

1.1 Golang Conversion

Name	Comment
Convert string to int	i, _ := strconv.ParseInt(“12345”, 10, 64)
Convert string to int	i, err := strconv.Atoi(“-42”)
Convert string to list	L := strings.Split(“hi,golang”, “”)
Convert string to []byte	`[]byte("abcXX")`
Convert string to byte	`byte(str1[])`
Convert byte to string	`string(byte('a'))=`
Convert string to float32	f, _ := strconv.ParseFloat(“3.1415”, 32)
Convert int to float32	0.5*float32(age)+7>= float32(age2)
Convert int to string	s := strconv.Itoa(-42). Notice: not `string(-42)`
Convert rune to string	`string(rune1)`
Convert string list to string	`strings.Join(list, ", ")`
Convert int list to string	`fmt.Sprintf("%s", l)`
Convert list to byte	byteI := byte(65)
Convert byte to int	`int(byte('a'))`
Convert byte to string	`string(byte('a'))`
Convert bytes to string	`string([]byte("abcXX"))`
Convert int32 to int32 Pointer	`func int32Ptr(i int32) *int32 { return &i }`
Convert string[] to string	`strings.Join([]string{"a", "b"}, ",")`
Format string	`fmt.Sprintf("%.3f", float64(v)/1000)`
Format string	`fmt.Sprintf("At %v, %s", e.When, e.What)`
Format string	`fmt.Printf("int: %d, float: %f, bool: %t\n", 123, 78.9, true)`

1.2 Deep Dive Into Golang

Go’s original target was networked system infrastructure, what we now call cloud software

Name	Comment
Golang goroutine
How Golang implement =defer=	Execute a piece of code before a function returns with FILO mechanism
How Golang implement timer
Golang for vs loop
Garbage Colection
Golang CSP vs Erlang Actor Model	Each actor model, which actor has its own queue
How Golang channel feature is implement?	YouTube: GopherCon 2017: Understanding Channels, Link: Golang Channel
Golang return a tuple	`func dfs(root TreeNode, max float64) (sum int, cnt int)`, LeetCode: Maximum Average Subtree
Use strings.Builder, instead of string	LeetCode: Unique Email Addresses
Variable Conversion	`float64(x_int/y_int)` != `float64(x_int)/float64(y_int)`, LeetCode: Maximum Average Subtree
For a list of objects, pass by value or reference	`f(l []TreeNode)` vs `f(l []*TreeNode)`, LeetCode: Lowest Common Ancestor of a Binary Tree

1.3 Golang Quality Improvement Tools

Name	Comment
gosec	Golang security checker, `gosec ./...`
golangci-lint	lint check, `golint`
errcheck	errcheck checks that you checked errors, `errcheck ./...`
delve	Delve is a debugger for the Go programming language.
ginkgo	BDD Testing Framework for Go
mock	GoMock is a mocking framework for Golang
envtest	provides libraries for integration testing by starting a local control plane
go-junit-report	Convert go test output to junit xml
gocover-cobertura	go tool cover to XML (Cobertura) export tool
gocovmerge	Merge coverprofile results from multiple go cover runs

1.4 Golang Dependencies

Name	Comment
goimports	updates your Go import lines, adding missing ones and removing unreferenced ones
dep	Go deps, now recommend `go modules`
Install go dep	`go get -u github.com/golang/dep/cmd/dep`
Go modules	export GO111MODULE=on, `go mod download`
Initialize new module in current directory	`go mod init XXX`
Download modules to local cache	`go mod download`
Add missing and remove unused modules	`go mod tidy`
Make vendored copy of dependencies	`go mod vendor`
Reference	Link: Using Go Modules

1.5 Golang Errors

Name	Comment
… does not support indexing	`variable[0]` -> `(variable)[0]`

1.6 Golang Common

Name	Comment
Upgrade golang to 1.12 in mac	`brew upgrade go`, `go version`
Reference	Link: The Go Programming Language Specification

1.7 Golang Code Structure & Common Algorithms

Name	Comment
Online Go Playgroud	https://play.golang.org/
One line if statement	if a >= 1 { fmt.Print(“yes”) }
Declare variables with initializers	var ischecked, v, str = false, 2, “yes!”
goroutine	Define functions to run as distince subprocesses
switch	code/example-switch.go
queue	LeetCode: Number of Recent Calls
bfs	code/tree-bfs.go
trie tree	code/tree-trie.go

1.8 Syntax Sugar: From Python To Golang

Name	Python	Golang
sum slice	`sum([1, 2, 3])`	sum := 0; for i := range nums { sum += nums[i] }
Get last item	`nums[-1]`	nums[len(nums)-1]
For	`for i in range(10):`	for i := 0; i < 10; i++
Loop list	`for num in [1, 2]`	for num := range[]int{1, 2} { fmt.Print(num) }
Loop string	`for ch in str:`	for _, ch := range str { fmt.Print(ch) }
Iterator	`for num in nums:`	for _, num := range nums {fmt.Print(num)}
While	`while isOK:`	`for isOK`
Check ch range	`ord(ch) in range(ord('a'), ord('z')+1)`	ch >=’a’ && ch <=’z’
Get min	`min(2, 6, 5)`
Check is nil	`root is None`	root == nil
Reverse list	`nums[::-1]`	Need to create your own function. Weird!

1.9 Surprises In Golang

Name	Comment
Modulus returns negative numbers	In golang, -3 % 2 == -1

1.10 Golang Array/List/Slice

Name	Comment
Make a array	var a [2]string; a[0]=”hello”; a[1]=”world”
Create array with given values	l := [6]int{2, 3, 7, 5, 11, 13}
Create array with given values	l := []string{“a”, “c”, “b”, “d”}
Create dynamically-sized arrays	a := make([]int, 5)
Create dynamically-sized arrays	a := make([]int, 1, 5) // 5 is capacity
Sort string array	`sort.Strings(l); fmt.Print(l)`
Sort int array	`sort.Ints(l)` //in-place change
Golang sort one array by another array	LeetCode: Largest Values From Labels
Sort in descending order	`sort.Sort(sort.Reverse(sort.IntSlice(keys)))`
Append item	l = append(l, “e”)
Append items	l = append(l, “e”, “b”, “c”)
Append item to head/prepend	`l = append([]string{"a"}, l...)`
Remove last item	`l = l[:len(l)-1]`
Remove item by index	`l = append(l[0:1], l[2:]...)`
Slices of a array	`var l2 = l[1:3]` // Notice: it’s a reference
Copy a list	b := make([]int, len(a)); copy(b, a)
Join two lists	`l1 = append(l1, l2...)`
Use pointer of array list	code/pointer-array.go

1.11 Golang String

Name	Comment
Format string	`fmt.Sprintf("At %v, %s", e.When, e.What)`
Format string	`fmt.Printf("int: %d, float: %f, bool: %t\n", 123, 78.9, true)`
Padding zero	`fmt.Printf("%02d:%02d", 2, 10)`
Split string	`var L = strings.Split("hi,golang", ",")`
Replace string	`var str2 = strings.Replace("hi,all", ",", ";", -1)`
Replace string	`strings.Replace("aaaa", "a", "b", 2)` //bbaa
Split string by separator	`strings.Split(path, " ")`
Count characters	`strings.Count("test", "t")`
Substring	`strings.Index("test", "e")`
Join string	`strings.Join([]string{"a","b"}, "-")`
Repeat string	`strings.Repeat("a", 2)` // aa
Lower string	`strings.ToLower("TEST")`
Trim whitespace in two sides	`strings.TrimSpace("\t Hello world!\n ")`
Trim trailing whitespace	`strings.TrimRight("\t Hello world!\n ", "\n ")`
Concact string	`fmt.Sprintf("%s%s", str1, str2)`
Reference	Link: package strings

1.12 Golang Integer/Float

Name	Comment
Int max	MaxInt32 = 1<<31 - 1 golang math
Int min	MinInt32 = -1 << 31 golang math
Pass int as reference	sample code

1.13 Golang Env

Name	Comment
GOPATH	It is called as the workspace directory for Go programs
GOROOT	The location of your Go installation. No need to set any more
`go env`	Show a full list of environment variables
Reference	Link: GOPATH, GOROOT, GOBIN

1.14 Golang Package management

Name	Comment
go mod	Link: go modules
go get fix	`GO111MODULE=off go get -fix ./...`
go mod replace url	go mod edit -replace…

1.15 Golang Ascii

Name	Comment
get character ascii	`byte('0')`
ascii offset	`fmt.Println(string('B' + byte('a')-byte('A')))`

1.16 Golang Dict/Hashmap/Map

Name	Comment
Create dict	`map[string]int{"a": 1, "b": 2}`
Create dict	`make(map[string]int)`
Check existence	_, ok := m[k]
Delete key	`delete(m, "k1")`
Create a map of lists	m := make(map[string][]string)
Get keys of a map	Loop the dictionary and append the key to a list
Use (x, y) as hashmap key	m[[2]int{2, 2}] = true, code/example-hashmap-arraykey.go

1.17 Golang Networking

Name	Comment
golang http	code/example-http.go

1.18 Golang Goroutines

Name	Comment
Basic goroutine	code/example-goroutine.go

1.19 Golang Inteface

Name	Comment
Hash map with both key and value dynamic	`map[interface{}]interface{}`
Define and use interface	code/example-interface.go
Convert map[interface {}]interface {} to map[string]string	code/interface-conversion.go

1.20 Golang Files & Folders

Name	Comment
Read files	code/example-read-file.go
Write files	code/example-write-file.go

1.21 Golang Math

Name	Comment
pow(2, 3)	`int(math.Pow(2, 3))` // Default is float64
sqrt	`math.Sqrt(100)`
Get rand	`rand.Intn(100)`, `rand.Float64()`

1.22 Golang Bit Operator & Math

Name	Comment
Shift left	`fmt.Print(1 << 10)` // 1024
Shift right	`fmt.Print(1024 >> 3)` // 128

1.23 Golang BBD Testing

Name	Summary
ginkgo	BDD Testing Framework for Go http://onsi.github.io/ginkgo/
Ubuntu install ginkgo	`apt-get install golang-ginkgo-dev`
gomega	Ginkgo’s Preferred Matcher Library
Add tags to tests	`// +build availability`, `go test -v --tags=availability ./test/e2e/...`

1.24 Golang Misc

Name	Comment
Golang sleep	`time.Sleep(4* time.Second)`
Golang logging	`import "log"=, =log.Info`, `log.Print`, `log.Error(err)`
Golang print function name	`runtime.Callers`

1.25 More Resources

https://play.golang.org/

https://tour.golang.org/list

https://golang.org/doc/

https://github.com/a8m/go-lang-cheat-sheet

License: Code is licensed under MIT License.

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1 Golang CheatSheet

1.1 Golang Conversion

1.2 Deep Dive Into Golang

1.3 Golang Quality Improvement Tools

1.4 Golang Dependencies

1.5 Golang Errors

1.6 Golang Common

1.7 Golang Code Structure & Common Algorithms

1.8 Syntax Sugar: From Python To Golang

1.9 Surprises In Golang

1.10 Golang Array/List/Slice

1.11 Golang String

1.12 Golang Integer/Float

1.13 Golang Env

1.14 Golang Package management

1.15 Golang Ascii

1.16 Golang Dict/Hashmap/Map

1.17 Golang Networking

1.18 Golang Goroutines

1.19 Golang Inteface

1.20 Golang Files & Folders

1.21 Golang Math

1.22 Golang Bit Operator & Math

1.23 Golang BBD Testing

1.24 Golang Misc

1.25 More Resources