slice添加map和filter方法

package main

import (
    "fmt"
    "strings"
)

// WorkWith会实现集合接口
type WorkWith struct {
    Data    string
    Version int
}

// Filter是一个过滤函数。
func Filter(ws []WorkWith, f func(w WorkWith) bool) []WorkWith {
    // 初始化返回值
    result := make([]WorkWith, 0)
    for _, w := range ws {
        if f(w) {
            result = append(result, w)
        }
    }
    return result
}

// Map是一个映射函数。
func Map(ws []WorkWith, f func(w WorkWith) WorkWith) []WorkWith {
    // 返回值的长度应该与传入切片长度一致
    result := make([]WorkWith, len(ws))
    for pos, w := range ws {
        newW := f(w)
        result[pos] = newW
    }
    return result
}

// LowerCaseData 将传入WorkWith的data字段变为小写
func LowerCaseData(w WorkWith) WorkWith {
    w.Data = strings.ToLower(w.Data)
    return w
}

// IncrementVersion 将传入WorkWith的Version加1
func IncrementVersion(w WorkWith) WorkWith {
    w.Version++
    return w
}

// OldVersion 返回一个闭包，用于验证版本是否大于指定的值
func OldVersion(v int) func(w WorkWith) bool {
    return func(w WorkWith) bool {
        return w.Version >= v
    }
}

func main() {
    ws := []WorkWith{
        {"Example", 1},
        {"Example 2", 2},
    }
    fmt.Printf("Initial list: %#v\n", ws)
    ws = Map(ws, LowerCaseData)
    fmt.Printf("After LowerCaseData Map: %#v\n", ws)
    ws = Map(ws, IncrementVersion)
    fmt.Printf("After IncrementVersion Map: %#v\n", ws)
    ws = Filter(ws, OldVersion(3))
    fmt.Printf("After OldVersion Filter: %#v\n", ws)
}