# Golang
## Summary
- Introduction
- [Hello World](#hello-world)
- [Go CLI Commands](#go-cli-commands)
- [Go Modules](#go-modules)
- Syntax
- [Basic Types](#basic-types)
- [Variables](#variables)
- [Operators](#operators)
- [Conditional Statements](#conditional-statements)
- [Loops](#loops)
- [Functions](#functions)
## Hello World
```go
package main
import "fmt"
func main() {
fmt.Println("Hello World!")
}
```
[Return to Summary](#summary)
## Go CLI Commands
```bash
# 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
```
[Return to Summary](#summary)
## 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**
```bash
# 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
[Return to Summary](#summary)
## 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 |
[Return to Summary](#summary)
## Variables
```go
// 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: ""
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
[Return to Summary](#summary)
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 | integers |
| `^` | 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 |
| `||` | Conditional OR |
| `!` | NOT |
[Return to Summary](#summary)
## Conditional Statements
```go
// 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'
}
```
[Return to Summary](#summary)
## Loops
```go
// 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 {
}
```
[Return to Summary](#summary)
## Functions
```go
// 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
// 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
```
[Return to Summary](#summary)