Learning Go - Tutorial From Official Documentation
There's something that doesn't click yet, just note down the ones that clicked or just info that make a bit of sense.
https://tour.golang.org/
Other References :
https://golang.org/pkg/
https://golang.org/ref/spec
https://golang.org/doc/articles/wiki/
https://blog.golang.org/
Google I/O 2012 - Go Concurrency Patterns - https://www.youtube.com/watch?v=f6kdp27TYZs
Google I/O 2013 - Advanced Go Concurrency Patterns - https://www.youtube.com/watch?v=QDDwwePbDtw
Go: a simple programming environment - https://vimeo.com/53221558
Note : I stopped at method, It's too much... Lol
Pointers
Go has pointers. A pointer holds the memory address of a value.
Structs
A struct is a collection of fields.
Struct Fields
Struct fields are accessed using a dot.
type Vertex struct {
X int
Y int
}
func main() {
v := Vertex{1, 2}
v.X = 4
fmt.Println(v.X)
}
Arrays
The type [n]T is an array of n values of type T.
var a [10]int # declares a variable a as an array of ten integers.func main() {
var a [2]string
a[0] = "Hello"
a[1] = "World"
fmt.Println(a[0], a[1])
fmt.Println(a)
primes := [6]int{2, 3, 5, 7, 11, 13}
fmt.Println(primes)
}my note : pretty straight forward... same as other array types in another language
Slices
An array has a fixed size. A slice, on the other hand, is a dynamically-sized, flexible view into the elements of an array. In practice, slices are much more common than arrays.
primes := [6]int{2, 3, 5, 7, 11, 13}
var s []int = primes[1:4]
fmt.Println(s)my note : I think this is the same as an array but can make a slice out of an array, but when you change one of the slice it affects the parent array.
A slice does not store any data, it just describes a section of an underlying array. Changing the elements of a slice modifies the corresponding elements of its underlying array. Other slices that share the same underlying array will see those changes.
func main() {
names := [4]string{
"John",
"Paul",
"George",
"Ringo",
}
fmt.Println(names)
a := names[0:2]
b := names[1:3]
fmt.Println(a, b)
b[0] = "XXX"
fmt.Println(a, b)
fmt.Println(names)
}Slice literals - A slice literal is like an array literal without the length.
func main() {
q := []int{2, 3, 5, 7, 11, 13}
fmt.Println(q)
r := []bool{true, false, true, true, false, true}
fmt.Println(r)
s := []struct {
i int
b bool
}{
{2, true},
{3, false},
{5, true},
{7, true},
{11, false},
{13, true},
}
fmt.Println(s)
}Slice defaults
var a [10]int
is equals to
a[0:10]
a[:10]
a[0:]
a[:]Slice length and capacity - A slice has both a length and a capacity. The length of a slice is the number of elements it contains. The capacity of a slice is the number of elements in the underlying array, counting from the first element in the slice. The length and capacity of a slice s can be obtained using the expressions len(s) and cap(s). You can extend a slice's length by re-slicing it, provided it has sufficient capacity. Try changing one of the slice operations in the example program to extend it beyond its capacity and see what happens.
func main() {
s := []int{2, 3, 5, 7, 11, 13}
printSlice(s)
// Slice the slice to give it zero length.
s = s[:0]
printSlice(s)
// Extend its length.
s = s[:4]
printSlice(s)
// Drop its first two values.
s = s[2:]
printSlice(s)
}
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}Nil slices - The zero value of a slice is nil. A nil slice has a length and capacity of 0 and has no underlying array.
func main() {
var s []int
fmt.Println(s, len(s), cap(s))
if s == nil {
fmt.Println("nil!")
}
}Creating a slice with make - Slices can be created with the built-in make function; this is how you create dynamically-sized arrays.
func main() {
a := make([]int, 5)
printSlice("a", a)
b := make([]int, 0, 5)
printSlice("b", b)
c := b[:2]
printSlice("c", c)
d := c[2:5]
printSlice("d", d)
}
func printSlice(s string, x []int) {
fmt.Printf("%s len=%d cap=%d %v\n",
s, len(x), cap(x), x)
}Slices of slices - Slices can contain any type, including other slices.
func main() {
// Create a tic-tac-toe board.
board := [][]string{
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
}
// The players take turns.
board[0][0] = "X"
board[2][2] = "O"
board[1][2] = "X"
board[1][0] = "O"
board[0][2] = "X"
for i := 0; i < len(board); i++ {
fmt.Printf("%s\n", strings.Join(board[i], " "))
}
}Appending to a slice - func append(s []T, vs ...T) []T
func main() {
var s []int
printSlice(s)
// append works on nil slices.
s = append(s, 0)
printSlice(s)
// The slice grows as needed.
s = append(s, 1)
printSlice(s)
// We can add more than one element at a time.
s = append(s, 2, 3, 4)
printSlice(s)
}
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}- Range - You can skip the index or value by assigning to
_.
for i, _ := range pow
for _, value := range pow- Function values - Functions are values too. They can be passed around just like other values. Function values may be used as function arguments and return values.
func compute(fn func(float64, float64) float64) float64 {
return fn(3, 4)
}
func main() {
hypot := func(x, y float64) float64 {
return math.Sqrt(x*x + y*y)
}
fmt.Println(hypot(5, 12))
fmt.Println(compute(hypot))
fmt.Println(compute(math.Pow))
}my note : so in main function can make function to a variable... hmm will be messy
Function closures - Go functions may be closures. A closure is a function value that references variables from outside its body. The function may access and assign to the referenced variables; in this sense the function is "bound" to the variables.
func adder() func(int) int {
sum := 0
return func(x int) int {
sum += x
return sum
}
}
func main() {
pos, neg := adder(), adder()
for i := 0; i < 10; i++ {
fmt.Println(
pos(i),
neg(-2*i),
)
}
}Methods
Go does not have classes. However, you can define methods on types. A method is a function with a special receiver argument. The receiver appears in its own argument list between the func keyword and the method name.
type Vertex struct {
X, Y float64
}
func (v Vertex) Abs() float64 {
return math.Sqrt(v.X*v.X + v.Y*v.Y)
}
func main() {
v := Vertex{3, 4}
fmt.Println(v.Abs())
}Methods are functions - Remember: a method is just a function with a receiver argument.
You can declare a method on non-struct types, too. In this example we see a numeric type MyFloat with an Abs method. You can only declare a method with a receiver whose type is defined in the same package as the method. You cannot declare a method with a receiver whose type is defined in another package (which includes the built-in types such as int).
type MyFloat float64
func (f MyFloat) Abs() float64 {
if f < 0 {
return float64(-f)
}
return float64(f)
}
func main() {
f := MyFloat(-math.Sqrt2)
fmt.Println(f.Abs())
}
Interfaces
An interface type is defined as a set of method signatures. A value of interface type can hold any value that implements those methods.
Interfaces are implemented implicitly - A type implements an interface by implementing its methods. There is no explicit declaration of intent, no "implements" keyword. Implicit interfaces decouple the definition of an interface from its implementation, which could then appear in any package without prearrangement.
Interface values - Under the hood, interface values can be thought of as a tuple of a value and a concrete type: (value, type) An interface value holds a value of a specific underlying concrete type. Calling a method on an interface value executes the method of the same name on its underlying type.
Nil interface values - A nil interface value holds neither value nor concrete type. Calling a method on a nil interface is a run-time error because there is no type inside the interface tuple to indicate which concrete method to call.
The empty interface - The interface type that specifies zero methods is known as the empty interface: interface{} An empty interface may hold values of any type. (Every type implements at least zero methods.) Empty interfaces are used by code that handles values of unknown type. For example, fmt.Print takes any number of arguments of type interface{}.
Things that I don't get [wtf]
- Pointers to structs - Struct fields can be accessed through a struct pointer.
- Struct Literals - A struct literal denotes a newly allocated struct value by listing the values of its fields.
- Range - The range form of the for loop iterates over a slice or map.
var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
func main() {
for i, v := range pow {
fmt.Printf("2**%d = %d\n", i, v)
}
}my notes : does this mean loop for pow ? variable v is inserted from pow ? where to limit to i loop ? does it automatically count the v as the limit ?
- Map - A map maps keys to values.
type Vertex struct {
Lat, Long float64
}
var m map[string]Vertex
func main() {
m = make(map[string]Vertex)
m["Bell Labs"] = Vertex{
40.68433, -74.39967,
}
fmt.Println(m["Bell Labs"])
}my note : whats the difference with an array?
- Map literals are like struct literals, but the keys are required.
type Vertex struct {
Lat, Long float64
}
var m = map[string]Vertex{
"Bell Labs": Vertex{
40.68433, -74.39967,
},
"Google": Vertex{
37.42202, -122.08408,
},
}
func main() {
fmt.Println(m)
}my note : when to use array, map or slice ?
Mutating Maps
Insert or update an element in map m:
m[key] = elem
Retrieve an element:
elem = m[key]
Delete an element:
delete(m, key)
Test that a key is present with a two-value assignment:
elem, ok = m[key]
If key is in m, ok is true. If not, ok is false.
If key is not in the map, then elem is the zero value for the map's element type.
Note: If elem or ok have not yet been declared you could use a short declaration form:
elem, ok := m[key]
func main() {
m := make(map[string]int)
m["Answer"] = 42
fmt.Println("The value:", m["Answer"])
m["Answer"] = 48
fmt.Println("The value:", m["Answer"])
delete(m, "Answer")
fmt.Println("The value:", m["Answer"])
v, ok := m["Answer"]
fmt.Println("The value:", v, "Present?", ok)
}Method : Pointer receivers - You can declare methods with pointer receivers. Methods with pointer receivers can modify the value to which the receiver points . Since methods often need to modify their receiver, pointer receivers are more common than value receivers.
type Vertex struct {
X, Y float64
}
func (v Vertex) Abs() float64 {
return math.Sqrt(v.X*v.X + v.Y*v.Y)
}
func (v *Vertex) Scale(f float64) {
v.X = v.X * f
v.Y = v.Y * f
}
func main() {
v := Vertex{3, 4}
v.Scale(10)
fmt.Println(v.Abs())
}