Golang入门——结构体、集合和高阶函数

结构体、集合和高阶函数

在应用中定义了一个结构体，可能需要这个结构体的对象集合，例如：

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

我们可以使用高阶函数，即把函数作为定义所需方法的参数。

func (cs Cars) Process(f func(car *Car)){
	for _,c := range cs{
		f(c)
	}
}

在上面基础上，实现一个查询函数来获取子集，并在 Process( ) 中传入一个闭包执行：

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  
}

实现 Map 功能，产出除 car 对象以外的东西：

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  
}

我们可以定义下面这样的具体查询：

allNewBMWs := allCars.FindAll(func(car *Car)bool{
	return (car.Manufacturer == "BMW") && (car.BuildYear > 2010)
})

我们可以根据参数返回不同的函数，也许我们向根据不同的厂商添加汽车到不同的集合，但是这可能是变化的。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：

func MakeSortedAppender(manufacturers []string)(func(car *Car),map[string]Cars){  
	sortedCars := make(map[string]Cars)  
	for _,m := range manufacturers{  
		sortedCars[m] = make([]*Car,0)  
	}  
  	sortedCars["Default"] = make([]*Car,0)  
  	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  
}

然后可以用它把汽车分类为独立的集合：

manufacturers := []string{"Ford","Aston Martin","Land Rover","BMW","Jaguar"}  
sortedAppender,sortedCars := MakeSortedAppender(manufacturers)  
allUnsortedCars.Process(sortedAppender)  
BMWCount := len(sortedCars["BMW"])

完整代码

package main  
  
import "fmt"  
type Any interface{}  
type Car struct{  
  Model string  
 Manufacturer string  
 BuildYear int  
}  
type Cars []*Car  
func (cs Cars) Process(f func(car *Car)){  
  for _,c := range cs{  
    f(c)  
  }  
}  
func print(car *Car){  
  fmt.Println(1,car)  
}  
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  
}  
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){  
  sortedCars := make(map[string]Cars)  
  for _,m := range manufacturers{  
    sortedCars[m] = make([]*Car,0)  
  }  
  sortedCars["Default"] = make([]*Car,0)  
  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  
}  
func main() {  
  ford := &Car{"Fiesta","Ford",2008}  
  bmw := &Car{"XL 450","BMW",2011}  
  merc := &Car{"D600","Mercedes",2009}  
  bmw2 := &Car{"X 800","BMW",2008}  
  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")  
}

输出结果：

AllCars: [0xc000064180 0xc0000641b0 0xc0000641e0 0xc000064210]
New BMWs: [0xc0000641b0]
Map sortedCars: map[Aston Martin:[] BMW:[0xc0000641b0 0xc000064210] Default:[0xc0000641e0] Ford:[0xc000064180] Jaguar:[] Land Rover:[]]
We have  2 BMWs

代码下载

以上程序代码均已上传到至github，有需要可直接进行下载