> For the complete documentation index, see [llms.txt](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ryanyang.gitbook.io/the-way-to-go-zh-cn/di-er-bu-fen-yu-yan-de-he-xin-jie-gou-yu-ji-shu/11.0/11.14.md). # 结构体、集合和高阶函数 通常你在应用中定义了一个结构体，那么你也可能需要这个结构体的（指针）对象集合，比如： ```go type Any interface{} type Car struct { Model string Manufacturer string BuildYear int // ... } type Cars []*Car ``` 在定义所需功能时我们可以利用函数可以作为（其它函数的）参数的事实来使用高阶函数，例如： 1）定义一个通用的 `Process()` 函数，它接收一个作用于每一辆 car 的 f 函数作参数： ```go // Process all cars with the given function f: func (cs Cars) Process(f func(car *Car)) { for _, c := range cs { f(c) } } ``` 2）在上面的基础上，实现一个查找函数来获取子集合，并在 `Process()` 中传入一个闭包执行（这样就可以访问局部切片 `cars`）： ```go // 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 } ``` 3）实现 Map 功能，产出除 car 对象以外的东西： ```go // 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 } ``` 现在我们可以定义下面这样的具体查询： ```go allNewBMWs := allCars.FindAll(func(car *Car) bool { return (car.Manufacturer == "BMW") && (car.BuildYear > 2010) }) ``` 4）我们也可以根据入参返回不同的函数。也许我们想根据不同的厂商添加汽车到不同的集合，但是这可能会是多变的。所以我们可以定义一个函数来产生特定的添加函数和 map 集： ```go 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 } ``` 现在我们可以用它把汽车分类为独立的集合，像这样： ```go manufacturers := []string{"Ford", "Aston Martin", "Land Rover", "BMW", "Jaguar"} sortedAppender, sortedCars := MakeSortedAppender(manufacturers) allUnsortedCars.Process(sortedAppender) BMWCount := len(sortedCars["BMW"]) ``` 我们让这些代码在下面的程序 cars.go 中执行： 示例 11.18 [cars.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_11/cars.go)： ```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, len(cs)) 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 } ``` 输出： ``` 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 ``` ## 链接 * [目录](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/directory.md) * 上一节：[Go 中的面向对象](/the-way-to-go-zh-cn/di-er-bu-fen-yu-yan-de-he-xin-jie-gou-yu-ji-shu/11.0/11.13.md) * 下一章：[读写数据](/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/12.0.md) --- # Agent Instructions This documentation is published with GitBook. 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