我可以键入断言一个接口值的切片? [英] Can I type assert a slice of interface values?
问题描述
我试图从 [] Node
中输入assert,以 Symbol
Node
接口。
这是一些周围的代码:
43 func applyLambda(args [] Node,env Env)Node {
44如果len(args)> 2 {
45 panic(无效参数计数)
46}
47 fixed,rest:= parseFormals(args。([] Symbol))
48 return Func {
49正文:args [1],
50 FixedVarNames:fixed,
51 RestVarName:rest,
52}
53}
$ c $ $ b ./builtins.go:47:invalid type assertion:args。([] Symbol)(非接口类型[]节点在左边)
我相信这有一个很好的理由。 c>变量 x
应该是接口类型,因为只有接口动态类型的变量才是固定的。虽然 Node
是一个接口,但是 [] Node
不是。切片是一种独特的非接口类型。因此,假设一片接口值也是一个接口也没有意义。
类型节点
在你的代码中有明确的定义,因此是一个接口。你已经为它指定了方法列表。类型 [] Node
不是那样。它定义了什么方法?
我明白你是从哪里来的。这可能是一个有用的捷径,但没有意义。这就好像期望 syms.Method()
在 syms
的类型为 []符号
和方法
用于符号
。
使用此代码替换第47行:
symbols:= make([] Symbol ,len(args))
for i,arg:= range args {symbols [i] = arg。(Symbol)}
fixed,rest:= parseFormals(symbols)
I am trying to type assert from a []Node
, to []Symbol
. In my code, Symbol
implements the Node
interface.
Here is some surrounding code:
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 }
Here's the error I get:
./builtins.go:47: invalid type assertion: args.([]Symbol) (non-interface type []Node on left)
I'm sure there's a good reason for this. What's the best way to proceed?
解决方案 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
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?
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
.
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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