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翻译11.14
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dake
@@ -8,13 +8,13 @@ OO 语言最重要的三个方面分别是：封装，继承和多态，在 Go
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1）包范围内的：通过标识符首字母小写，`对象`只在它所在的包内可见
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2）可导出的：通过标识符首字母大写，`对象`在所在包以外可见
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2）可导出的：通过标识符首字母大写，`对象`对所在包以外也可见
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类型只拥有自己所在包中定义的方法。
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- 继承：用组合实现：内嵌一个（或多个）包含想要行为（字段和方法）的类型；多重继承可以通过内嵌多个类型实现
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- 继承：用组合实现：内嵌一个（或多个）包含想要的行为（字段和方法）的类型；多重继承可以通过内嵌多个类型实现
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- 多态：用接口实现：某个类型的实例可以赋给它实现的任意接口的变量。类型和接口是松耦合的，并且多重继承可以通过实现多个接口达到。Go 接口不是 Java 和 C# 接口的变体，而且：接口间是不相关的，并且是大规模编程和可适应演进型设计的关键。
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- 多态：用接口实现：某个类型的实例可以赋给它所实现的任意接口类型的变量。类型和接口是松耦合的，并且多重继承可以通过实现多个接口实现。Go 接口不是 Java 和 C# 接口的变体，而且：接口间是不相关的，并且是大规模编程和可适应的演进型设计的关键。
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## 链接
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214
eBook/11.14.md
214
eBook/11.14.md
@@ -1,2 +1,216 @@
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# 结构体，集合和高阶函数
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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：
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```go
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type Any interface{}
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type Car struct {
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Model string
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Manufacturer string
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BuildYear int
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// ...
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}
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type Cars []*Car
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```
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我们可以用函数定义所需的功能有争议的事实来使用高阶函数，例如：
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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：
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```go
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// Process all cars with the given function f:
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func (cs Cars) Process(f func(car *Car)) {
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for _, c := range cs {
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f(c)
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}
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}
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```
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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`）：
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```go
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// Find all cars matching a given criteria.
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func (cs Cars) FindAll(f func(car *Car) bool) Cars {
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cars := make([]*Car, 0)
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cs.Process(func(c *Car) {
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if f(c) {
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append(cars,c)
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}
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)
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return cars
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}
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```
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3）实现一个 Map 功能，产出除了 car 对象以外的东西：
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```go
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// Process cars and create new data.
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func (cs Cars) Map(f func(car *Car) Any) []Any {
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result := make([]Any, 0)
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ix := 0
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cs.Process(func(c *Car) {
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result[ix] = f(c)
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ix++
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})
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return result
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}
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```
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现在我们可以定义下面这样的具体查询：
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```go
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allNewBMWs := allCars.FindAll(func(car *Car) bool {
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return (car.Manufacturer == “BMW”) && (car.BuildYear > 2010)
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})
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```
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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：
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```go
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funcMakeSortedAppender(manufacturers[]string)(func(car*Car),map[string]Cars) {
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// Prepare maps of sorted cars.
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sortedCars := make(map[string]Cars)
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for _, m := range manufacturers {
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sortedCars[m] = make([]*Car, 0)
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}
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sortedCars[“Default”] = make([]*Car, 0)
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// Prepare appender function:
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appender := func(c *Car) {
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if _, ok := sortedCars[c.Manufacturer]; ok {
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sortedCars[c.Manufacturer] = append(sortedCars[c.Manufacturer], c)
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} else {
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sortedCars[“Default”] = append(sortedCars[“Default”], c)
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}
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}
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return appender, sortedCars
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}
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```
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现在我们可以用它来把汽车分为独立的集合，像这样：
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```go
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manufacturers := []string{“Ford”, “Aston Martin”, “Land Rover”, “BMW”, “Jaguar”}
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sortedAppender, sortedCars := MakeSortedAppender(manufacturers)
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allUnsortedCars.Process(sortedAppender)
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BMWCount := len(sortedCars[“BMW”])
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```
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我们让这些代码在下面的程序 cars.go（此外只展示了 main() 中的代码，别的代码已经在上面展示）中执行：
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示例 11.18 [cars.go](examples/chapter_11/cars.go)：
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```go
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// cars.go
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package main
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import (
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"fmt"
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)
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type Any interface{}
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type Car struct {
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Model string
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Manufacturer string
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BuildYear int
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// ...
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}
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type Cars []*Car
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func main() {
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// make some cars:
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ford := &Car{"Fiesta","Ford", 2008}
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bmw := &Car{"XL 450", "BMW", 2011}
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merc := &Car{"D600", "Mercedes", 2009}
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bmw2 := &Car{"X 800", "BMW", 2008}
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// query:
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allCars := Cars([]*Car{ford, bmw, merc, bmw2})
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allNewBMWs := allCars.FindAll(func(car *Car) bool {
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return (car.Manufacturer == "BMW") && (car.BuildYear > 2010)
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})
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fmt.Println("AllCars: ", allCars)
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fmt.Println("New BMWs: ", allNewBMWs)
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//
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manufacturers := []string{"Ford", "Aston Martin", "Land Rover", "BMW", "Jaguar"}
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sortedAppender, sortedCars := MakeSortedAppender(manufacturers)
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allCars.Process(sortedAppender)
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fmt.Println("Map sortedCars: ", sortedCars)
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BMWCount := len(sortedCars["BMW"])
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fmt.Println("We have ", BMWCount, " BMWs")
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}
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// Process all cars with the given function f:
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func (cs Cars) Process(f func(car *Car)) {
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for _, c := range cs {
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f(c)
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}
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}
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// Find all cars matching a given criteria.
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func (cs Cars) FindAll(f func(car *Car) bool) Cars {
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cars := make([]*Car, 0)
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cs.Process(func(c *Car) {
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if f(c) {
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cars = append(cars, c)
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}
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})
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return cars
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}
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// Process cars and create new data.
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func (cs Cars) Map(f func(car *Car) Any) []Any {
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result := make([]Any, 0)
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ix := 0
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cs.Process(func(c *Car) {
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result[ix] = f(c)
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ix++
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})
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return result
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}
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func MakeSortedAppender(manufacturers []string) (func(car *Car), map[string]Cars) {
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// Prepare maps of sorted cars.
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sortedCars := make(map[string]Cars)
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for _, m := range manufacturers {
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sortedCars[m] = make([]*Car, 0)
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}
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sortedCars["Default"] = make([]*Car, 0)
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// Prepare appender function:
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appender := func(c *Car) {
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if _, ok := sortedCars[c.Manufacturer]; ok {
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sortedCars[c.Manufacturer] = append(sortedCars[c.Manufacturer], c)
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} else {
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sortedCars["Default"] = append(sortedCars["Default"], c)
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}
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}
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return appender, sortedCars
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}
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/* Output:
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AllCars: [0xf8400038a0 0xf840003bd0 0xf840003ba0 0xf840003b70]
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New BMWs: [0xf840003bd0]
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Map sortedCars: map[Default:[0xf840003ba0] Jaguar:[] Land Rover:[] BMW:[0xf840003bd0 0xf840003b70] Aston Martin:[] Ford:[0xf8400038a0]]
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We have 2 BMWs
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*/
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```
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## 链接
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- [目录](directory.md)
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- 上一节：[Go 中的面向对象](11.13.md)
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- 下一章：[读写数据](12.0.md)
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@@ -107,6 +107,7 @@
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- 11.11 [Printf 和反射](11.11.md)
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- 11.12 [接口与动态类型](11.12.md)
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- 11.13 [总结：Go 中的面向对象](11.13.md)
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- 11.14 [结构体，集合和高阶函数](11.14.md)
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## 第三部分：Go 高级编程
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