英文:
How to define a type constraint for any channel type
问题
我正在尝试定义一个函数，该函数返回给定通道使用率的百分比：
func ChannelUsagePct[T any](channel chan T) int {
channelCap := cap(channel)
channelLen := len(channel)
if channelCap == 0 {
// 无缓冲通道
return 0
}
return 100 * channelLen / channelCap
}
func main() {
twoWayChannel := make(chan int, 10)
var sendOnlyChannel chan<- int = twoWayChannel
var recvOnlyChannel <-chan int = twoWayChannel
fmt.Println(ChannelUsagePct(twoWayChannel))
fmt.Println(ChannelUsagePct(sendOnlyChannel)) // 不起作用
fmt.Println(ChannelUsagePct(recvOnlyChannel)) // 不起作用
}
现在的问题是，这个函数对于第一个通道有效，但对于第二个和第三个通道无效，而不改变函数的签名。但是，如果我改变签名，我需要选择通道是只接收还是只发送。有没有一种定义零通道的方法？例如，不能读取也不能写入，我只想在其上使用cap和len函数。
理想情况下，ChannelUsagePct应该适用于这三种情况中的任何一种。
英文:
I'm trying to define a funcion that returns the percentage of usage of a given channel:
func ChannelUsagePct[T any](channel chan T) int {
channelCap := cap(channel)
channelLen := len(channel)
if channelCap == 0 {
// Unbuffered channel
return 0
}
return 100 * channelLen / channelCap
}
func main() {
twoWayChannel := make(chan int, 10)
var sendOnlyChannel chan<- int = twoWayChannel
var recvOnlyChannel <-chan int = twoWayChannel
fmt.Println(ChannelUsagePct(twoWayChannel))
fmt.Println(ChannelUsagePct(sendOnlyChannel)) // Does not work
fmt.Println(ChannelUsagePct(recvOnlyChannel)) // Does not work
}
Now the thing is that this works for the first channel but not for the second and third, without changing the func's signature. But if I change the signature, I need to either choose the channel to be receive only, or send only. Is there a way to define a channel that is zero-way? E.g. cannot be read nor written to, I just want to use cap and len funcs on it.
Ideally the ChannelUsagePct should work for any of the 3 cases.
答案1
得分: 3
为了允许通道的三种可能形式，需要定义一个单独的类型约束。
type Chan[T any] interface {
chan T | <-chan T | chan<- T
}
当使用时，需要使用类型参数将类型约束实例化为T的类型：
func Cap[T any, C Chan[T]](c C) int {
return cap(c)
}
由于实例化的存在，无法推断整个类型，只需要提供通道元素类型：
ch := make(chan int, 3)
i := Cap[int](ch)
fmt.Println(i)
// 3
https://go.dev/play/p/1lx5R4MFvFx
英文:
In order to allow all three possible forms of a channel, a separate type constraint needs to be defined.
type Chan[T any] interface {
chan T | <-chan T | chan<- T
}
This will require instantiating the type constraint with the type of T when it's used, which can be done with another type parameter:
func Cap[T any, C Chan[T]](c C) int {
return cap(c)
}
Because of that instantiation the entire type cannot be inferred, but only the channel element type needs to be supplied:
ch := make(chan int, 3)
i := Cap[int](ch)
fmt.Println(i)
// 3
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