Learn Go - Maps and Structs examples

maps_structs.go

// Map examples, Struct examples
package main

import (
	"fmt"
	"reflect"
)

// used for checking tags

type Doctor struct {
	number     int
	Name       string // Doctor.Name is visible outside the package
	companions []string
}

type Surgeon struct {
	Doctor
	tools string `required max:"100"` // tagged for ensuring this does not exceed a max of 100
}

func main() {
	statePopulations := map[string]int{
		"California":   39393,
		"Pennsynvania": 45454,
		"New Jersey":   11223,
	}

	fmt.Println(statePopulations)
	fmt.Println(statePopulations["California"])

	// can use make to make an empty map
	newMap := make(map[string]int)
	newMap["newKey"] = 888
	fmt.Println(newMap["newKey"])

	// Note: return order of maps is random, vs a slice or array which maintains order
	// You can also delete a key
	delete(newMap, "newKey")
	check, ok := newMap["newKey"] // if a key does not exist, it will automatically return 0, and set the 'ok' var
	fmt.Println(check, ok)

	// copying maps share the same object
	sp := statePopulations
	delete(sp, "New Jersey")
	fmt.Println(statePopulations)
	fmt.Println(sp)

	// using a struct
	aDoctor := Doctor{
		number: 3,
		Name:   "John",
		companions: []string{
			"PersonA",
			"PersonB",
			"PersonC",
		},
	}
	fmt.Println(aDoctor)
	fmt.Println(aDoctor.Name)
	fmt.Println(aDoctor.companions[2])

	// anonymous structure
	newDoc := struct{ name string }{name: "My Name"}
	fmt.Println(newDoc)

	// Go supports composition via embedding - VERSUS TRADITIONAL OOP / CLASS INHERITANCE
	// Note, Surgeon IS NOT a Doctor, it HAS a Doctor component but it is not the same
	// While methods can carry through in this way, generally it is better to leverage interfaces for this
	aSurgeon := Surgeon{}
	aSurgeon.number = 10
	aSurgeon.Name = "Toby"
	aSurgeon.companions = []string{"Tom", "John"}
	aSurgeon.tools = "Slicer"

	fmt.Println(aSurgeon)

	// Access the struct tag
	t := reflect.TypeOf(Surgeon{})
	field, _ := t.FieldByName("tools")
	fmt.Println(field.Tag) // you can parse this value to test the actual value of this member
}