英文:
How to iterate over a union of slices passed in a generic function? (T has no core type)
问题
我正在测试 Go 1.18 中的泛型，并查看了这个示例。
我想重新创建该示例，但是希望能够传入一个 int 切片或 float 切片，并在函数中将切片中的所有元素相加。
当我尝试迭代切片时遇到了一些问题。这是我尝试的代码：
package main
import "fmt"
// NumberSlice 约束
type NumberSlice interface {
[]int64 | []float64
}
func add[N NumberSlice](n N) {
// 希望：遍历 n 并打印 v 的值
for _, v := range n {
fmt.Println(v)
}
}
func main() {
ints := []int64{1, 2}
add(ints)
}
我得到了错误信息：
无法对 n 进行迭代（N 的类型受 NumberSlice 约束）（N 没有核心类型）
我该如何实现这个功能？
英文:
I am testing out generics in go 1.18 and took a look at this example.
I would like to recreate that example but instead be able to pass in a slice of int or slice of float instead, and in the function I'll just sum up everything in the slice.
This is when I ran into some issues just iterating the slice. This is what I tried:
package main
import "fmt"
// NumberSlice constraint
type NumberSlice interface {
[]int64 | []float64
}
func add[N NumberSlice](n N) {
// want: to range over n and print value of v
for _, v := range n {
fmt.Println(v)
}
}
func main() {
ints := []int64{1, 2}
add(ints)
}
I got the error:
> cannot range over n (variable of type N constrained by NumberSlice) (N has no core type)
How do I accomplish this?
答案1
得分: 9
一个核心类型，对于一个接口（包括接口约束），定义如下：
如果满足以下条件之一，接口T具有核心类型：
存在一个单一类型
U，它是T类型集中所有类型的底层类型或者T的类型集仅包含具有相同元素类型E的通道类型，并且所有定向通道具有相同的方向。
你的接口约束没有核心类型，因为它有两个底层类型：[]int64和[]float64。
因此，在需要核心类型的地方，你不能使用它。特别是range和make。
你可以将接口更改为要求基本类型，然后在函数签名中指定切片：
// 仍然没有核心类型...
type Number interface {
int64 | float64
}
// ...但是参数将实例化为int64或float64
func add[N Number](n []N) {
for _, v := range n {
fmt.Println(v)
}
}
这也可以工作，但更冗长：
type NumberSlice[N int64 | float64] interface {
// 一个核心类型 []N
~[]N
}
func add[S NumberSlice[N], N int64 | float64](n S) {
for _, v := range n {
fmt.Println(v)
}
}
英文:
A core type, for an interface (including an interface constraint) is defined as follows:
> An interface T has a core type if one of the following conditions is
> satisfied:
>
> - There is a single type U which is the underlying type of all types in the type set of T
>
> - or the type set of T contains only channel types with identical element type E, and all directional channels have the same direction.
Your interface constraint has no core type, because it has two underlying types: []int64 and []float64.
Therefore you can't use it where a core type is required. Notably range and make.
You can change the interface to require the base types, and then specify the slice in the function signature:
// still no core type...
type Number interface {
int64 | float64
}
// ...but the argument will be instantiated with either int64 or float64
func add[N Number](n []N) {
for _, v := range n {
fmt.Println(v)
}
}
This also works, but it's way more verbose:
type NumberSlice[N int64 | float64] interface {
// one core type []N
~[]N
}
func add[S NumberSlice[N], N int64 | float64](n S) {
for _, v := range n {
fmt.Println(v)
}
}
答案2
得分: 1
这样的代码对你有用吗？
package main
import "fmt"
type NumberOrFloat interface {
int64 | float64
}
func add[N NumberOrFloat](n []N) {
for _, v := range n {
fmt.Println(v)
}
}
func main() {
ints := []int64{1, 2}
add(ints)
}
这里的区别在于你对数组元素定义了类型约束（而不是数组类型）：[]N
英文:
Could something like this work for you?
package main
import "fmt"
type NumberOrFloat interface {
int64 | float64
}
func add[N NumberOrFloat](n []N) {
for _, v := range n {
fmt.Println(v)
}
}
func main() {
ints := []int64{1, 2}
add(ints)
}
The difference here is that you define type constraints on array elements (not on array types): []N
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