generics - 复制 slice 的通用方法

Question

我需要复制 slice (和底层数组的一部分)，这样调用者就不会改变数组的原始元素。我想我可以编写一个函数来为特定类型的数组执行此操作:

func duplicateSliceOfSomeType(sliceOfSomeType []SomeType) []SomeType {
    dulicate := make([]SomeType, len(sliceOfSomeType))
    copy(duplicate, sliceOfSomeType)
    return duplicate
}

但是有没有一种方法可以通用地创建相同的方法，也许不需要泛型？

func duplicateSlice(slice []?) []?{
    duplicate := make([]?, len(slice))
    copy(duplicate, slice)
    return duplicate
}

Answer 1

你可以写一个简单的语句来制作一个 slice 的浅拷贝，

b := append([]T(nil), a...)

相当于，

b := make([]T, len(a))
copy(b, a)

例如，

package main

import "fmt"

type T int

func main() {
    a := []T{4, 2}

    b := append([]T(nil), a...)

    fmt.Println(&a[0], a, &b[0], b)
    b[0] = 9
    fmt.Println(&a[0], a, &b[0], b)
}

输出:

0x10328000 [4 2] 0x10328020 [4 2]
0x10328000 [4 2] 0x10328020 [9 2]

附录:

Common difficulties with reflection

If people are new to Go, they shouldn't be using reflection at all.

-rob

Reflection is subtle even for experts. It exposes details whose understanding depends on knowing pretty fundamental things about how the language works and, to a lesser extent, how it is implemented. It can be bewildering even for experienced Go programmers; for newly minted Gophers there are much more important, simpler things to learn first. Those who learn reflection too early confuse themselves cloud their understanding of those fundamentals. Best to keep it at arm's length until the rest of the picture is clear.

-rob

也就是说，

package main

import (
    "fmt"
    "reflect"
)

func CopySlice(s interface{}) interface{} {
    t, v := reflect.TypeOf(s), reflect.ValueOf(s)
    c := reflect.MakeSlice(t, v.Len(), v.Len())
    reflect.Copy(c, v)
    return c.Interface()
}

type T int

func main() {

    {
        // append
        a := []T{4, 2}
        b := append([]T(nil), a...)
        fmt.Println(&a[0], a, &b[0], b)
        b[0] = 9
        fmt.Println(&a[0], a, &b[0], b)
    }

    {
        // make and copy
        a := []T{4, 2}
        b := make([]T, len(a))
        copy(b, a)
        fmt.Println(&a[0], a, &b[0], b)
        b[0] = 9
        fmt.Println(&a[0], a, &b[0], b)
    }

    {
        // reflection
        a := []T{4, 2}
        b := CopySlice(a).([]T)
        fmt.Println(&a[0], a, &b[0], b)
        b[0] = 9
        fmt.Println(&a[0], a, &b[0], b)
    }

}

输出:

0xc20800a200 [4 2] 0xc20800a210 [4 2]
0xc20800a200 [4 2] 0xc20800a210 [9 2]
0xc20800a290 [4 2] 0xc20800a2a0 [4 2]
0xc20800a290 [4 2] 0xc20800a2a0 [9 2]
0xc20800a310 [4 2] 0xc20800a320 [4 2]
0xc20800a310 [4 2] 0xc20800a320 [9 2]