typescript 散列变量语法在打字稿中是如何工作的？
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How does the hash variable syntax work in typescript?
提问by Doug
...and where is it documented?
......它在哪里记录？
I've seen examples like this around the place:
我在这个地方看到过这样的例子：
class MyThing {
private _layers: { [id: string] : SimpleLayer } = {};
...
}
...and that works, which is great, but the syntax is confusing to me.
...这是有效的，这很棒，但语法让我感到困惑。
What is 'id'? Why is the syntax not just blah:{string:SimpleLayer}, which doesnt work. I've also seen {[name: string]:Type} and {[index:string]:Type}.
什么是“身”？为什么语法不只是 blah:{string:SimpleLayer}，它不起作用。我还看到了 {[name: string]:Type} 和 {[index:string]:Type}。
I've been looking over typescriptlang.org trying to find where this is actually documented, but I can't seem to find it at all.
我一直在查看 typescriptlang.org 试图找到实际记录的位置，但我似乎根本找不到它。
回答by JLRishe
TypeScript Walkthrough: Interfaces
See the section "Describing an Indexable Object". This is called an index signature.
请参阅“描述可索引对象”一节。这称为索引签名。
The syntax for defining the index is:
定义索引的语法是：
[Identifier: KeyType]: ValueType
KeyTypecan be either stringor number.
KeyType可以是string或number。
You could claim that the Identifierisn't really needed since it doesn't get used anywhere, but I think it's required in order to force the class/interface designer to indicate what the hash map key should represent (an id, name, e-mail address, etc.). This also provides the possibility of having intellisense show the hash key name (as Visual Studio does for other languages), though I don't think Typescript intellisense currently provides this.
您可以声称它Identifier并不是真正需要的，因为它不会在任何地方使用，但我认为这是强制类/接口设计器指示哈希映射键应表示的内容（id、名称、e-邮件地址等）。这也提供了让智能感知显示哈希键名称的可能性（就像 Visual Studio 对其他语言所做的那样），尽管我认为 Typescript 智能感知目前没有提供这一点。
回答by meagar
Regarding your question of why the syntax isn't simpler, specifically something like blah:{string:SimpleLayer}:
关于你为什么语法不简单的问题，特别是这样的blah:{string:SimpleLayer}：
Because this would be ambiguous. This syntax already exists and has meaning:
因为这将是模棱两可的。此语法已存在并具有以下含义：
var x: { string: SimpleLayer }
This declares a variable x. The type of xhas one property, named string, which is of type SimpleLayer. If I wanted to use x, I would do this:
这声明了一个变量x。的类型x有一个名为 的属性string，它的类型为SimpleLayer。如果我想使用x，我会这样做：
x.string = new SimpleLayer;
It's more obvious if we use a real example:
如果我们使用一个真实的例子就更明显了：
var circle: {radius: number}
This declares a variable with one property (radius) that is of type number, it does notdeclare a hash mapping radiustypes to numbertypes.
这声明了一个具有一个属性 ( radius)的变量number，它是 type ，它没有声明radius类型到number类型的哈希映射。
