the-way-to-go_ZH_CN/eBook/examples/chapter_11/cars.go

// cars.go
package main

import (
	"fmt"
)


type Any interface{}
type Car struct {
	Model   	string
	Manufacturer	string
	BuildYear	int
    // ...
}
type Cars []*Car

func main() {
	// make some cars:
	ford := &Car{"Fiesta","Ford", 2008}
	bmw  := &Car{"XL 450", "BMW", 2011}
	merc := &Car{"D600", "Mercedes", 2009}
	bmw2 := &Car{"X 800", "BMW", 2008}
	// query:
	allCars := Cars([]*Car{ford, bmw, merc, bmw2})
	allNewBMWs := allCars.FindAll(func(car *Car) bool {
      return (car.Manufacturer == "BMW") && (car.BuildYear > 2010)
	})
	fmt.Println("AllCars: ", allCars)
	fmt.Println("New BMWs: ", allNewBMWs)
	//
	manufacturers := []string{"Ford", "Aston Martin", "Land Rover", "BMW", "Jaguar"}
	sortedAppender, sortedCars := MakeSortedAppender(manufacturers)
	allCars.Process(sortedAppender)
	fmt.Println("Map sortedCars: ", sortedCars)
    BMWCount := len(sortedCars["BMW"])
	fmt.Println("We have ", BMWCount, " BMWs")
}

// Process all cars with the given function f:
func (cs Cars) Process(f func(car *Car)) {
     for _, c := range cs {
         f(c)
     }
}

// Find all cars matching a given criteria.
func (cs Cars) FindAll(f func(car *Car) bool) Cars {
    cars := make([]*Car, 0)

    cs.Process(func(c *Car) {
        if f(c) {
            cars = append(cars, c)
        }
    })
    return cars
}

// Process cars and create new data.
func (cs Cars) Map(f func(car *Car) Any) []Any {
       result := make([]Any, 0)
       ix := 0
       cs.Process(func(c *Car) {
           result[ix] = f(c)
           ix++
       })
       return result
}

func MakeSortedAppender(manufacturers []string) (func(car *Car), map[string]Cars) {
     // Prepare maps of sorted cars.
       sortedCars := make(map[string]Cars)
   
       for _, m := range manufacturers {
           sortedCars[m] = make([]*Car, 0)
       }
       sortedCars["Default"] = make([]*Car, 0)
   
       // Prepare appender function:
       appender := func(c *Car) {
           if _, ok := sortedCars[c.Manufacturer]; ok {
               sortedCars[c.Manufacturer] = append(sortedCars[c.Manufacturer], c)
           } else {
               sortedCars["Default"] = append(sortedCars["Default"], c)
           }
       }
       return appender, sortedCars
}

/* Output:
AllCars:  [0xf8400038a0 0xf840003bd0 0xf840003ba0 0xf840003b70]
New BMWs:  [0xf840003bd0]
Map sortedCars:  map[Default:[0xf840003ba0] Jaguar:[] Land Rover:[] BMW:[0xf840003bd0 0xf840003b70] Aston Martin:[] Ford:[0xf8400038a0]]
We have  2  BMWs
*/