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docs: start libs section of go cheatsheet

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languages/golang.md
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@ -2,32 +2,37 @@
## Summary ## Summary
- Introduction - Introduction
- [Hello World](#hello-world) - [Hello World](#hello-world)
- [Go CLI Commands](#go-cli-commands) - [Go CLI Commands](#go-cli-commands)
- [Go Modules](#go-modules) - [Go Modules](#go-modules)
- Basic - Basic
- [Basic Types](#basic-types) - [Basic Types](#basic-types)
- [Variables](#variables) - [Variables](#variables)
- [Operators](#operators) - [Operators](#operators)
- [Conditional Statements](#conditional-statements) - [Conditional Statements](#conditional-statements)
- [Loops](#loops) - [Loops](#loops)
- [Arrays](#arrays) - [Arrays](#arrays)
- [Functions](#functions) - [Functions](#functions)
- Advanced - Advanced
- [Structs](#structs) - [Structs](#structs)
- [Maps](#maps) - [Maps](#maps)
- [Pointers](#pointers) - [Pointers](#pointers)
- [Methods and Interfaces](#methods-and-interfaces)
- [Errors](#errors)
- [Testing](#testing)
- Standard Libs
- [Package fmt](#package-fmt)
## Hello World ## Hello World
```go ```go
package main package main
import "fmt" import "fmt"
func main() { func main() {
fmt.Println("Hello World!") fmt.Println("Hello Gophers!")
} }
``` ```
@ -44,7 +49,7 @@ $ go run [file.go]
# Compile # Compile
$ go build [file.go] $ go build [file.go]
# Running compiled file # Running compiled file
$ ./hello $ ./hello
# Test packages # Test packages
$ go test [folder] $ go test [folder]
@ -80,16 +85,17 @@ $ go version
## Go Modules ## Go Modules
- Go projects are called **modules** - Go projects are called **modules**
- Each module has multiple **packages** - Each module has multiple **packages**
- Each package should has a scoped functionality. Packages talk to each other to compose the code - 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** - A module needs at least one package, the **main**
- The package main needs a entry function called **main** - The package main needs a entry function called **main**
```bash ```bash
# Create Module # Create Module
$ go mod init [name] $ go mod init [name]
``` ```
Tip: By convention, modules names has the follow structure: Tip: By convention, modules names has the follow structure:
domain.com/user/module/package domain.com/user/module/package
@ -102,25 +108,25 @@ Example: github.com/spf13/cobra
## Basic Types ## Basic Types
| Type | Set of Values | Values | | Type | Set of Values | Values |
|:---------:|:-----------------:|:---------:| | :--------: | :----------------------------------------: | :-------------------------------------------: |
| bool | boolean | true/false | | bool | boolean | true/false |
| string | array of characters | needs to be inside "" | | string | array of characters | needs to be inside "" |
| int | integers | 32 or 64 bit integer | | int | integers | 32 or 64 bit integer |
| int8 | 8-bit integers | [ -128, 128 ] | | int8 | 8-bit integers | [ -128, 128 ] |
| int16 | 16-bit integers | [ -32768, 32767] | | int16 | 16-bit integers | [ -32768, 32767] |
| int32 | 32-bit integers | [ -2147483648, 2147483647] | | int32 | 32-bit integers | [ -2147483648, 2147483647] |
| int64 | 64-bit integers | [ -9223372036854775808, 9223372036854775807 ] | | int64 | 64-bit integers | [ -9223372036854775808, 9223372036854775807 ] |
| uint8 | 8-bit unsigned integers | [ 0, 255 ] | | uint8 | 8-bit unsigned integers | [ 0, 255 ] |
| uint16 | 16-bit unsigned integers | [ 0, 65535 ] | | uint16 | 16-bit unsigned integers | [ 0, 65535 ] |
| uint32 | 32-bit unsigned integers | [ 0, 4294967295 ] | | uint32 | 32-bit unsigned integers | [ 0, 4294967295 ] |
| uint64 | 64-bit unsigned integers | [ 0, 18446744073709551615 ] | | uint64 | 64-bit unsigned integers | [ 0, 18446744073709551615 ] |
| float32 | 32-bit float | | | float32 | 32-bit float | |
| float64 | 64-bit float | | | float64 | 64-bit float | |
| complex64 | 32-bit float with real and imaginary parts | | | complex64 | 32-bit float with real and imaginary parts | |
| complex128 | 64-bit float with real and imaginary parts | | | complex128 | 64-bit float with real and imaginary parts | |
| byte | sets of bits | alias for uint8 | | byte | sets of bits | alias for uint8 |
| rune | Unicode characters | alias for int32 | | rune | Unicode characters | alias for int32 |
[Return to Summary](#summary) [Return to Summary](#summary)
@ -130,7 +136,7 @@ Example: github.com/spf13/cobra
```go ```go
// Declaration // Declaration
var int value var int value
// Initialization // Initialization
value = 10 value = 10
@ -171,7 +177,7 @@ const pi = 3.1415
[Return to Summary](#summary) [Return to Summary](#summary)
Arithmetic Operators Arithmetic Operators
| Symbol | Operation | Valid Types | | Symbol | Operation | Valid Types |
|:---------:|:-------------:|:-------------:| |:---------:|:-------------:|:-------------:|
| `+` | Sum | integers, floats, complex values, strings | | `+` | Sum | integers, floats, complex values, strings |
| `-` | Difference | integers, floats, complex values | | `-` | Difference | integers, floats, complex values |
@ -186,7 +192,7 @@ Arithmetic Operators
| `>>` | Right shift | integer >> unsigned integer | | `>>` | Right shift | integer >> unsigned integer |
Comparison Operators Comparison Operators
| Symbol | Operation | | Symbol | Operation |
|:---------:|:-------------:| |:---------:|:-------------:|
| `==` | Equal | | `==` | Equal |
| `!=` | Not equal | | `!=` | Not equal |
@ -196,7 +202,7 @@ Comparison Operators
| `>=` | Greater or equal | | `>=` | Greater or equal |
Logical Operators Logical Operators
| Symbol | Operation | | Symbol | Operation |
|:---------:|:-------------:| |:---------:|:-------------:|
| `&&` | Conditional AND | | `&&` | Conditional AND |
| `||` | Conditional OR | | `||` | Conditional OR |
@ -250,7 +256,7 @@ switch text {
// 'Byee' // 'Byee'
default: default:
// 'Ok' // 'Ok'
} }
// Switch without condition // Switch without condition
value := 5 value := 5
@ -262,7 +268,7 @@ switch {
// 'Byee' // 'Byee'
default: default:
// 'Ok' // 'Ok'
} }
``` ```
[Return to Summary](#summary) [Return to Summary](#summary)
@ -295,7 +301,7 @@ for {
<hr/> <hr/>
## Arrays ## Arrays
```go ```go
// Declaration with specified size // Declaration with specified size
@ -334,9 +340,9 @@ slice := make([]int, 5, 6) // make(type, len, cap)
// Append new element to slice // Append new element to slice
slice := []int{ 1, 2 } slice := []int{ 1, 2 }
slice = append(slice, 3) slice = append(slice, 3)
slice // { 1, 2, 3 } slice // { 1, 2, 3 }
slice = append(slice, 3, 2, 1) slice = append(slice, 3, 2, 1)
slice // { 1, 2, 3, 3, 2, 1 } slice // { 1, 2, 3, 3, 2, 1 }
// For range: iterate over a slice // For range: iterate over a slice
slice := string["W", "o", "w"] slice := string["W", "o", "w"]
@ -362,6 +368,7 @@ for _, value := range slice {
<hr/> <hr/>
## Functions ## Functions
```go ```go
// Functions acts as a scoped block of code // Functions acts as a scoped block of code
func sayHello() { func sayHello() {
@ -402,7 +409,7 @@ func switchValuesAndDouble(x, y int) {
} }
a, b = 2, 5 a, b = 2, 5
switchValuesAndDouble(2, 5) switchValuesAndDouble(2, 5)
// a = 10 // a = 10
// b = 4 // b = 4
@ -424,7 +431,7 @@ func mult(x, y int) int {
calc(sum) // 8 calc(sum) // 8
calc(mult) // 12 calc(mult) // 12
// Function closures: a function that returns a function // Function closures: a function that returns a function
// that remembers the original context // that remembers the original context
func calc() func(int) int { func calc() func(int) int {
value := 0 value := 0
@ -539,4 +546,116 @@ Obs: Unlike C, Go doesn't have pointer arithmetics.
[Return to Summary](#summary) [Return to Summary](#summary)
<hr/>
## Methods and Interfaces
Go doesn't have classes. But you can implement methods, interfaces and almost everything contained in OOP, but in what gophers call "Go Way"
```go
type Dog struct {
Name string
}
func (dog *Dog) bark() string {
return dog.Name + " is barking!"
}
dog := Dog{"Rex"}
dog.bark() // Rex is barking!
```
Interfaces are implicitly implemented. You don't need to inform that your struct are correctly implementing a interface if it already has all methods with the same name of the interface.
All structs implement the `interface{}` interface. This empty interface means the same as `any`.
```go
// Car implements Vehicle interface
type Vehicle interface {
Accelerate()
}
type Car struct {
}
func (car *Car) Accelerate() {
return "Car is moving on ground"
}
```
[Return to Summary](#summary)
<hr/>
## Errors
Go doesn't support `throw`, `try`, `catch` and other common error handling structures. Here, we use `error` package to build possible errors as a returning parameter in functions
```go
import "errors"
// Function that contain a logic that can cause a possible exception flow
func firstLetter(text string) (string, error) {
if len(text) < 1 {
return nil, errors.New("Parameter text is empty")
}
return string(text[0]), nil
}
a, errorA := firstLetter("Wow")
a // "W"
errorA // nil
b, errorB := firstLetter("")
b // nil
errorB // Error("Parameter text is empty")
```
[Return to Summary](#summary)
<hr/>
## Testing
Go has a built-in library to unit testing. In a separate file you insert tests for functionalities of a file and run `go test package` to run all tests of the actual package or `go test path` to run a specific test file.
```go
// main.go
func Sum(x, y int) int {
return x + y
}
// main_test.go
import (
"testing"
"reflect"
)
func TestSum(t *testing.T) {
x, y := 2, 4
expected := 2 + 4
if !reflect.DeepEqual(sum(x, y), expected) {
t.Fatalf("Function Sum not working as expected")
}
}
```
[Return to Summary](#summary)
<hr/>
## Package `fmt`
```go
import "fmt"
fmt.Print("Hello World") // Print in console
fmt.Println("Hello World") // Print and add a new line in end
fmt.Printf("%s is %d years old", "John", 32) // Print with formatting
fmt.Errorf("User %d not found", 123) // Print a formatted error
```
[Return to Summary](#summary)
<hr/> <hr/>