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programming:go [2023/11/01 07:31] – removed - external edit (Unknown date) 127.0.0.1programming:go [2023/11/01 07:31] (current) – ↷ Page moved from camunda:programming:go to programming:go skipidar
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 +===== GO ======
 +
 +Go is a replacement of C, C++.
 +
 +Go has some advantages when building simple, little services. \\
 +Simple language to build simle services.
 +
 +So this language has API and syntax support for solving current prolems.\\
 +For microservices you need less polymorpism, but more concurency and verbosity.\\
 + - Build in concurrency. No mutex.
 + - Building for any platform
 + - Consistent API. Helpful when updating to new versions.
 + - One way to do things - less static code analysis needed
 +
 +
 +IDE: Gogland
 +https://www.jetbrains.com/go/
 +
 +There is a youtube channel about GO. HelloWorld, tooling,.. \\
 +https://www.youtube.com/channel/UC_BzFbxG2za3bp5NRRRXJSw
 +
 +==== Commands ====
 +
 +Basic executable
 +<sxh go>
 +package main
 +
 +func main() {
 + println("hello")
 +}
 +</sxh>
 +
 +==Build command==
 +
 +<sxh go>
 +// in windows - builds a win application
 +go build -o mywin.exe
 +
 +// or in ubuntu - builds a linux app
 +go build -o myfirstexecutable
 +</sxh>
 +
 +
 +==Run command==
 +
 +Build and executes
 +
 +<sxh go>
 +$ go run main.go
 +hello
 +</sxh>
 +
 +
 +==Docs of StandardLib==
 +https://pkg.go.dev/std
 +
 +==GO packages==
 +
 +
 +for imports
 +
 +https://pkg.go.dev/
 +
 +==GO modules loading==
 +
 +Loading a module and tidy up dependencies
 +
 +<sxh go>
 +$ go get github.com/jboursiquot/go-proverbs
 +go mod tidy
 +</sxh>
 +
 +
 +==GO private public functions==
 +
 +Capitized functions - are public.
 +
 +small letter functions - are private.
 +
 +<sxh go>
 +
 +//public
 +func Fprintln(w io.Writer, a ...any) (n int, err error) {
 + p := newPrinter()
 + p.doPrintln(a)
 + n, err = w.Write(p.buf)
 + p.free()
 + return
 +}
 +
 +
 +// private
 +func newPrinter() *pp {
 + p := ppFree.Get().(*pp)
 + p.panicking = false
 + p.erroring = false
 + p.wrapErrs = false
 + p.fmt.init(&p.buf)
 + return p
 +}
 +
 +</sxh>
 +
 +
 +
 +==Naked return==
 +
 +Naked return. The name of the variable to return is defined in the method signature as "greeting"
 +
 +<sxh go>
 +
 +// greetWithNameAndAge returns a greeting with the name and age
 +func greetWithNameAndAge(name string, age int) (greeting string) {
 + greeting = "Hello, my name is " + name + " and I am " + strconv.Itoa(age) + " years old."
 + return
 +}
 +
 +</sxh>
 +
 +
 +== Return multiple values ==
 +
 +Ya can retrurn multiple value
 +
 +<sxh go>
 +func vals() (int, int) {
 + return 3, 7
 +}
 +
 +func main() {
 + a, b := vals()
 + fmt.Println(a)
 + fmt.Println(b)
 +}
 +</sxh>
 +
 +==Return multiple value - with errors ==
 +
 +The first value is returned, when there is no error.
 +
 +
 +<sxh go>
 +func divide(a, b int) (int, error) {
 + if b == 0 {
 + return 0, errors.New("cannot divide by zero")
 + }
 + return a / b, nil
 +}
 +</sxh>
 +
 +
 +== Variables ==
 +
 +The ''':=''' short variable assignment operator indicates that short variable declaration is being used. There is no need to use the var keyword or declare the variable type.
 +
 +
 +<sxh go>
 +
 +package main
 +
 +import (
 + "fmt"
 + "github.com/jboursiquot/proverbs"
 + "strconv"
 +)
 +
 +// package variables
 +var x, y, z bool = true, true, true
 +
 +// accesses the package level values
 +func packlvlvars() (bool, bool, bool) {
 + return x, y, z
 +}
 +
 +func main() {
 +
 + // method variables
 + // below vars are covering the package-level values in the scope of current function
 +
 +
 + // long variant
 + // split declaration and assignment
 + var mvar int
 + mvar = 123
 + fmt.Println(mvar)
 +
 +
 + // combine declaration and assignment
 + var mvar2 int = 123
 + fmt.Println(mvar2)
 +
 +
 + // declare multiple
 + x, y, z := 1, 2, "bla"
 + fmt.Println(strconv.Itoa(x) + strconv.Itoa(y) + z)
 +
 + // need a special value to get package variables
 + a, b, c := packlvlvars()
 + fmt.Println(strconv.FormatBool(a) + strconv.FormatBool(b) + strconv.FormatBool(c))
 +
 +}
 +
 +
 +</sxh>
 +
 +
 +== Pointers ==
 +
 +
 +<sxh go>
 +// basic-types/pointers/end/main.go
 +package main
 +
 +import (
 + "fmt"
 + "reflect"
 +)
 +
 +func main() {
 + // create a variable of type *T where T is an int
 + var a *int
 +
 + // declare and assign `b` variable of type int
 + valu := 100
 +
 + // assign the address of b to a
 + pointr = &valu
 +
 + // print out the value of a which is the address of b
 + fmt.Println(pointr)
 + // returns: ptr
 + fmt.Println("Type: %s", reflect.ValueOf(pointr).Kind() )
 +
 + // print out the value at the address of b
 + fmt.Println(*pointr)
 +}
 +</sxh>
 +
 +
 +== Structs & pass by reference or value ==
 +
 +Structure to hold data in Go Lang
 +
 +
 +
 +
 +<sxh go>
 +type author struct {
 + first string
 + last  string
 +}
 +
 +// getter 
 +// attention - the assignment to struct - is derived from parenthesis after "func" keyword
 +// is declared OUTSIDE of struct :(
 +func (a author) fullName() string {
 + return a.first + " " + a.last
 +}
 +
 +// setter
 +// passing the reference, so that we change the exact object and not its value
 +// changeName changes the first and last name of the author
 +func (a *author) changeName(first, last string) {
 + a.first = first
 + a.last = last
 +}
 +
 +func main() {
 + // initialize author
 + a := author{
 + first: "Marcus",
 + last:  "Aurelius",
 + }
 +
 + // print the author's full name
 + fmt.Println(a.fullName())
 +}
 +
 +</sxh>
 +
 +''*address'' - passes by reference
 +
 +Explains why to pass 
 +
 +{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/lzCAcBclf3.png?529x226}}
 +