英文:
Interface literals in Go
问题
首先澄清一下标题，我知道Go语言中没有接口字面量这样的东西，但我想不出其他名称来描述这个问题。
我在阅读一些Go代码时发现了一个奇怪的结构，如下所示：
clientOptions := []grpc.DialOption{grpc.WithInsecure()}
cc, err := grpc.Dial(l.Addr().String(), clientOptions...)
这里的grpc.DialOption是一个接口类型，grpc.WithInsecure()返回的就是这个类型。引起我的注意的是clientOptions是一个切片，这对我来说似乎是多余的。所以我尝试去掉大括号，像这样：
clientOptions := grpc.DialOption{grpc.WithInsecure()}
但是我得到了编译错误："invalid composite literal type grpc.DialOption"
我在Go Playground上尝试模拟这个问题，结果得到了相同的错误。
这段代码可以正常运行：
https://go.dev/play/p/QJQR9BDGN4a
但是这个版本在编译时失败，出现了相同的"invalid composite literal type"错误：
https://go.dev/play/p/A0FasDybUg5
有人能解释一下这是为什么吗？
谢谢。
英文:
First to clarify the title, I know there is no such thing as interface literals in Go but I couldn't come up with another name for this issue.
I was reading some Go code and found a weird construct, like so:
clientOptions := []grpc.DialOption{grpc.WithInsecure()}
cc, err := grpc.Dial(l.Addr().String(), clientOptions...)
Here grpc.DialOptions is an interface type and grpc.WithInsecure() returns that type. What caught my eye here is that clientOptions is a slice, which seemed redundant to me. So I tried to remove the braces like so:
clientOptions := grpc.DialOption{grpc.WithInsecure()}
But I get compilation error: "invalid composite literal type grpc.DialOption"
I tried to simulate this on the go playground and I get the same result.
This code runs fine:
https://go.dev/play/p/QJQR9BDGN4a
But this version fails with the same "invalid composite literal type error":
https://go.dev/play/p/A0FasDybUg5
Can someone explain this?
Thanks
答案1
得分: 0
你是正确的，这创建了一个切片：
clientOptions := []grpc.DialOption{grpc.WithInsecure()}
但是我认为你误解了哪个语法做了什么。这将是一个空的切片字面量：
clientOptions := []grpc.DialOption{}
这将是一个单个值，不在切片中：
clientOptions := grpc.WithInsecure()
供参考，这种语法在《Go之旅》中有介绍（https://tour.golang.org/）。
英文:
You are correct that this creates a slice:
clientOptions := []grpc.DialOption{grpc.WithInsecure()}
But I think you've misunderstood which syntax does what. This would be an empty slice literal:
clientOptions := []grpc.DialOption{}
This would be a single value, not in a slice:
clientOptions := grpc.WithInsecure()
For reference, this syntax is covered in the Tour of Go.
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