typescript 数组_TypeScript元组

typescript 数组

Sometimes we like to store values in an array with specific types. Using the any type can of course solve this problem but it will also allow certain types we might not want. This where tuples come in.

有时我们喜欢将值存储在具有特定类型的数组中。 当然，使用any类型可以解决此问题，但它也允许某些我们可能不想要的类型。 元组进入的地方。

Say we want to create a user array of a userName and a userId;

假设我们要创建一个userName和userId的user数组；

let user: any;
let userId = 1;
let userName = "Alf";

let randomBoolean = true;

user = [userId, userName]; // valid
user = [userId, randomBoolean]; // also valid

By setting our user to be of the any type, we can assign any type to it and this defeats our purpose of having a userId which is a number and a userName which is a string type. We can use a tuple to solve this.

通过将user设置为any类型，我们可以为其分配任何类型，这违背了我们的目的：使用userId作为number ，使用userName作为string类型。 我们可以使用元组来解决这个问题。

let user: [number,string];
let userId = 1;
let userName = "Alf";
let randomBoolean = true;

user = [userId, userName]; // valid
user = [userId, randomBoolean]; // error: Type 'true' is not assignable to type 'string'

We define a tuple by putting our intended types into square brackets and comma-separated, in this case, a number and a string. Now if we pass-in a type that isn’t defined in the tuple, say a boolean, we get an error message that says:

我们通过将预期类型放入方括号并用逗号分隔(在这种情况下为number和string定义元组 。 现在，如果我们传入未在元组中定义的类型，例如boolean ，则会收到一条错误消息，内容为：

Type ‘true’ is not assignable to type 'string’.

类型“ true”不可分配给“字符串”类型。

This is because we defined our tuple to accept a string as it’s second input but we passed in a boolean.

这是因为我们将元组定义为接受string作为第二个输入，但是我们传入了boolean 。

访问元组中的元素 (Accessing elements in a tuple)

To access an element in a tuple, we use it’s index just like in an array.

要访问元组中的元素，我们就像在数组中一样使用它的索引。

console.log(user[0])  // 1
console.log(user[1])  // Alf

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Tuples become very useful when we want to create a dictionary or a key-value pair. Using our example from above, we can have an array of user names and their ids without mistakenly passing in a different type to create problems later.

当我们要创建字典或键值对时，元组变得非常有用。 使用上面的示例，我们可以拥有一个用户名及其ID数组，而不会错误地传入其他类型以以后产生问题。

let users: [number, string][] = [[1,"Alf"],[2,"Jane"],[3,"Nii"]];

When assigning values to a tuple, the first two values must match exactly the types defined in the tuple.

将值分配给元组时，前两个值必须与元组中定义的类型完全匹配。

For example, in our example above, our first element has to be a number and the second, a string. If we interchange the values, we will get an error even though their types have been defined in the tuple.

例如，在上面的示例中，我们的第一个元素必须是number ，第二个元素必须是string 。 如果我们交换值，即使在元组中定义了它们的类型，我们也会得到一个错误。

let user: [number,string];
user = ["Alf", 1]; // invalid

The above code is invalid because, user expects the first element to be a number and the second a string, but not vice-versa.

上面的代码无效，因为user希望第一个元素是number ，第二个元素是string ，反之亦然。

Any subsequent value we add to the tuple variable can be any of the predefined tuple types in no particular order.

我们添加到tuple变量的任何后续值都可以是任何预定义的tuple类型，而没有特定的顺序。

user[2] = "John"; // valid
user[3] = 4; // valid
user[4] = true; // invalid.

In the above code, because the tuple was declared with a number and a string, we can input an element of either the string or number in no order provided they aren’t the first two elements. We still can’t assign a boolean value to an element because the tuple wasn’t declared with a boolean type.

在上面的代码中，由于元组是用number和string ，因此我们可以按任意顺序输入string或number的元素，只要它们不是前两个元素即可。 我们仍然无法为元素分配boolean值，因为未使用boolean类型声明元组。

That’s it. Hope you found this post useful. ✨

而已。 希望您发现这篇文章有用。 ✨

翻译自: https://www.digitalocean.com/community/tutorials/typescript-tuples

typescript 数组