9.6 KiB
9.6 KiB
Golang
Summary
- Introduction
- Basic
- Advanced
Hello World
package main
import "fmt"
func main() {
fmt.Println("Hello World!")
}
Go CLI Commands
# Compile & Run code
$ go run [file.go]
# Compile
$ go build [file.go]
# Running compiled file
$ ./hello
# Test packages
$ go test [folder]
# Install packages/modules
$ go install [package]
# List installed packages/modules
$ go list
# Update packages/modules
$ go fix
# Format package sources
$ go fmt
# See package documentation
$ go doc [package]
# Add dependencies and install
$ go get [module]
# See Go environment variables
$ go env
# See version
$ go version
Go Modules
- Go projects are called modules
- Each module has multiple packages
- Each package should has a scoped functionality. Packages talk to each other to compose the code
- A module needs at least one package, the main
- The package main needs a entry function called main
# Create Module
$ go mod init [name]
Tip: By convention, modules names has the follow structure:
domain.com/user/module/package
Example: github.com/spf13/cobra
Basic Types
| Type | Set of Values | Values |
|---|---|---|
| bool | boolean | true/false |
| string | array of characters | needs to be inside "" |
| int | integers | 32 or 64 bit integer |
| int8 | 8-bit integers | [ -128, 128 ] |
| int16 | 16-bit integers | [ -32768, 32767] |
| int32 | 32-bit integers | [ -2147483648, 2147483647] |
| int64 | 64-bit integers | [ -9223372036854775808, 9223372036854775807 ] |
| uint8 | 8-bit unsigned integers | [ 0, 255 ] |
| uint16 | 16-bit unsigned integers | [ 0, 65535 ] |
| uint32 | 32-bit unsigned integers | [ 0, 4294967295 ] |
| uint64 | 64-bit unsigned integers | [ 0, 18446744073709551615 ] |
| float32 | 32-bit float | |
| float64 | 64-bit float | |
| complex64 | 32-bit float with real and imaginary parts | |
| complex128 | 64-bit float with real and imaginary parts | |
| byte | sets of bits | alias for uint8 |
| rune | Unicode characters | alias for int32 |
Variables
// Declaration
var int value
// Initialization
value = 10
// Declaration + Initialization + Type inference
var isActive = true
// Short declaration (only inside functions)
text := "Hello"
// Multi declaration
var i, j, k = 1, 2, 3
// Variable not initialized = Zero values
// Numeric: 0
// Boolean: false
// String: ""
// Special value: nil (same as null)
var number int // 0
var text string // false
var boolean bool // ""
// Type conversions
// T(v) converts v to type T
i := 1.234 // float
int(i) // 1
// Constants
const pi = 3.1415
Operators
Arithmetic Operators
| Symbol | Operation | Valid Types |
|---|---|---|
+ |
Sum | integers, floats, complex values, strings |
- |
Difference | integers, floats, complex values |
* |
Product | integers, floats, complex values |
/ |
Quotient | integers, floats, complex values |
% |
Remainder | integers |
& |
Bitwise AND | integers |
| ` | ` | Bitwise OR |
^ |
Bitwise XOR | integers |
&^ |
Bit clear (AND NOT) | integers |
<< |
Left shift | integer << unsigned integer |
>> |
Right shift | integer >> unsigned integer |
Comparison Operators
| Symbol | Operation |
|---|---|
== |
Equal |
!= |
Not equal |
< |
Less |
<= |
Less or equal |
> |
Greater |
>= |
Greater or equal |
Logical Operators
| Symbol | Operation |
|---|---|
&& |
Conditional AND |
| ` | |
! |
NOT |
Conditional Statements
// If / Else
i := 1
if i > 0 {
// Condition is True! i is greater than zero
} else {
// Condition is False! i is lower or equal to zero
}
// Else if
i := 1
if i > 0 {
// Condition is True! i is greater than zero
} else if i > 0 && i < 2 {
// Condition is True! i greater than zero and lower than two
} else if i > 1 && i < 4 {
// Condition is True! i greater than one and lower than four
} else {
// None of the above conditions is True, so it falls here
}
// If with short statements
i := 2.567
if j := int(i); j == 2 {
// Condition is True! j, the integer value of i, is equal to two
} else {
// Condition is False! j, the integer value of i, is not equal to two
}
// Switch
text := 'hey'
switch text {
case 'hey':
// 'Hello!'
case 'bye':
// 'Byee'
default:
// 'Ok'
}
// Switch without condition
value := 5
switch {
case value < 2:
// 'Hello!'
case value >= 2 && value < 6:
// 'Byee'
default:
// 'Ok'
}
Loops
// Golang only has the for loop
for i := 0; i < 10; i++ {
// i
}
// The first and third parameters are ommitable
// For as a while
i := 0;
for i < 10 {
i++
}
// Forever loop
for {
}
Arrays
// Declaration with specified size
var array [3]string
array[0] = "Hello"
array[1] = "Golang"
array[2] = "World"
// Declaration and Initialization
values := [5]int{1, 2, 3, 4, 5}
// Slices: A subarray that acts as a reference of an array
// Determining min and max
values[1:3] // {2, 3, 4}
// Determining only max will use min = 0
values[:2] // {1, 2, 3}
// Determining only min will use max = last element
values[3:] // {3, 4}
// Length: number of elements that a slice contains
len(values) // 5
// Capacity: number of elements that a slice can contain
values = values[:1]
len(values) // 2
cap(values) // 5
// Slice literal
slice := []bool{true, true, false}
// make function: create a slice with length and capacity
slice := make([]int, 5, 6) // make(type, len, cap)
// Append new element to slice
slice := []int{ 1, 2 }
slice = append(slice, 3)
slice // { 1, 2, 3 }
slice = append(slice, 3, 2, 1)
slice // { 1, 2, 3, 3, 2, 1 }
// For range: iterate over a slice
slice := string["W", "o", "w"]
for i, value := range slice {
i // 0, then 1, then 2
value // "W", then "o", then "w"
}
// Skip index or value
for i := range slice {
i // 0, then 1, then 2
}
for _, value := range slice {
value // "W", then "o", then "w"
}
Functions
// Functions acts as a scoped block of code
func sayHello() {
// Hello World!
}
sayHello() // Hello World!
// Functions can take zero or more parameters, as so return zero or more parameters
func sum(x int, y int) int {
return x + y
}
sum(3, 7) // 10
// Returned values can be named and be used inside the function
func doubleAndTriple(x int) (double, triple int) {
double = x * 2
triple = x * 3
return
}
d, t := doubleAndTriple(5)
// d = 10
// t = 15
// Skipping one of the returned values
_, t := doubleAndTriple(3)
// t = 9
// Functions can defer commands. Defered commands are
// runned in a stack order after the execution and
// returning of a function
var aux = 0
func switchValuesAndDouble(x, y int) {
aux = x
defer aux = 0 // cleaning variable to post use
x = y * 2
y = aux * 2
}
a, b = 2, 5
switchValuesAndDouble(2, 5)
// a = 10
// b = 4
// aux = 0
// Functions can be handled as values
func calc(fn func(int, int) int) int {
return fn(2, 6)
}
func sum(x, y int) int {
return x + y
}
func mult(x, y int) int {
return x * y
}
calc(sum) // 8
calc(mult) // 12
// Function closures: a function that returns a function
// that remembers the original context
func calc() func(int) int {
value := 0
return func(x int) int {
value += x
return value
}
}
calculator := calc()
calculator(3) // 3
calculator(45) // 48
calculator(12) // 60
Structs
Structs are a way to arrange data in specific formats.
// Declaring a struct
type Person struct {
Name string
Age int
}
// Initializing
person := Person{"John", 34}
person.Name // "John"
person.Age // 34
person2 := Person{Age: 20}
person2.Name // ""
person2.Age // 20
person3 := Person{}
person3.Name // ""
person3.Age // 0
Maps
Maps are data structures that holds values assigneds to a key.
// Declaring a map
var cities map[string]string
// Initializing
cities = make(map[string]string)
cities // nil
// Insert
cities["NY"] = "EUA"
// Retrieve
newYork = cities["NY"]
newYork // "EUA"
// Delete
delete(cities, "NY")
// Check if a key is setted
value, ok := cities["NY"]
ok // false
value // ""
Pointers
Pointers are a direct reference to a memory address that some variable or value is being stored.
// Pointers has *T type
var value int
var pointer *int
// Point to a variable memory address with &
value = 3
pointer = &value
pointer // 3
pointer = 20
pointer // 20
pointer += 5
pointer // 25
// Pointers to structs can access the attributes
type Struct struct {
X int
}
s := Struct{3}
pointer := &s
s.X // 3
Obs: Unlike C, Go doesn't have pointer arithmetics.