我可以键入断言一部分接口值吗? [英] Can I type assert a slice of interface values?

问题描述

我正在尝试从 []Node 到 []Symbol 键入断言.在我的代码中，Symbol 实现了 Node 接口.

I am trying to type assert from a []Node, to []Symbol. In my code, Symbol implements the Node interface.

这里是一些周边代码:

 43 func applyLambda(args []Node, env Env) Node {
 44     if len(args) > 2 {
 45         panic("invalid argument count")
 46     }
 47     fixed, rest := parseFormals(args.([]Symbol))
 48     return Func{
 49         Body: args[1],
 50         FixedVarNames: fixed,
 51         RestVarName: rest,
 52     }
 53 }

这是我得到的错误:

./builtins.go:47: invalid type assertion: args.([]Symbol) (non-interface type []Node on left)

我相信这是有充分理由的.最好的方法是什么?

I'm sure there's a good reason for this. What's the best way to proceed?

推荐答案

话说x.(T)变量x应该是接口类型的，因为只针对变量类型接口动态类型不固定.虽然 Node 是一个接口，但 []Node 不是.切片是一种独特的非接口类型.所以假设接口值的一部分也是一个接口是没有意义的.

In saying x.(T) variable x should be of interface type, because only for variables of type interface dynamic type is not fixed. And while Node is an interface, []Node is not. A slice is a distinct, non-interface type. So it just doesn't make sense to assume a slice of interface values is an interface too.

Type Node 在你的代码中有明确的定义，因此是一个接口.您已经为其指定了方法列表.类型 []Node 不是那样的.它定义了哪些方法?

Type Node has a clear definition in your code and thus is an interface. You have specified the list of methods for it. Type []Node isn't like that. What methods does it define?

我了解您的出处.这可能是一个有用的捷径，但没有任何意义.这有点像期望 syms.Method() 在 syms 的类型是 []Symbol 和 Method 时工作> 代表符号.

I understand where your are coming from with this. It may be a useful shortcut, but just doesn't make sense. It's kind of like expecting syms.Method() to work when syms's type is []Symbol and Method is for Symbol.

用此代码替换第 47 行即可:

Replacing line 47 with this code does what you want:

symbols := make([]Symbol, len(args))
for i, arg := range args { symbols[i] = arg.(Symbol) }
fixed, rest := parseFormals(symbols)

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