typescript：固定大小数组的接口

Is there a way in typescript define fixed size array. say, for example, in a function definition, I need to able to say

在typescript中有一种方法定义固定大小的数组。比方说，例如，在函数定义中，我需要能够说

coord: (c:any) => number[]; //how to say it is an array of size 4

can I define an interface like we define a hash map

我可以像定义哈希映射一样定义接口

//this doesn't work
interface IArray{
  [number]
}

and also restrict max length to be 4.

并且还将最大长度限制为4。

3 个解决方案

#1

It's sort of awkward, but you can do it like this:

这有点尴尬，但你可以这样做：

interface SizeFour<T> {
    0: T;
    1: T;
    2: T;
    3: T;
}

function fn(): SizeFour<string> {
    // Need to cast
    return <any>['', '', '', ''];   
}

var x = fn();
var a = x[0]; // a: string
var b = x[4]; // b: any; error if --noImplicitAny

#2

You could return a tuple instead of an array:

你可以返回一个元组而不是一个数组：

type array_of_4 = [number, number, number, number];

var myFixedLengthArray :array_of_4 = [1,2,3,4];

// the tuple can be used as an array:
console.log(myFixedLengthArray.join(','));

#3

Preventing someone from using an index into an array outside the bounds is not something that even C# can do. e.g. what is preventing you from doing :

防止有人在索引之外的数组中使用索引不是C＃可以做的事情。例如什么阻止你做：

var index = 123; 
sizeFour[index];

Or even requesting the index from the server?

甚至从服务器请求索引？

So short answer "there isn't a declarative way of preventing this if you insist on using []"

如此简短的回答“如果你坚持使用[]，就没有一种预防性的方法可以防止这种情况发生。

You could always do

你可以随时做

var bar = {
   one : 'something',
   two: 'somethingelse'
   // etc. 
}

and then only use . i.e. bar.one

然后才使用。即bar.one

#1