> For the complete documentation index, see [llms.txt](https://zenofchain.gitbook.io/sway-bian-cheng-yu-yan-geng-xin-zhong-the-sway-programming-languageupdatin/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://zenofchain.gitbook.io/sway-bian-cheng-yu-yan-geng-xin-zhong-the-sway-programming-languageupdatin/6.-gao-ji-gai-nian-advanced-concepts/6.1-gao-ji-lei-xing-advanced-types.md).

# 6.1 高级类型 (Advanced Types)

### 用类型别名创建类型同义词 (Creating Type Synonyms with Type Aliases)

Sway provides the ability to declare a type alias to give an existing type another name. For this we use the `type` keyword. For example, we can create the alias `Kilometers` to `u64` like so:

Sway提供了声明一个类型别名的能力，进而给现有的类型另一个名字。为此我们使用`type`关键字。例如，我们可以创建`Kilometers`到`u64`的别名，像这样：

```
type Kilometers = u64;

```

Now, the alias `Kilometers` is a *synonym* for `u64`. Note that `Kilometers` is **not** a separate new type. Values that have the type `Kilometers` will be treated the same as values of type `u64`:

现在，别名 `Kilometers`是 `u64`的 \_同义词。请注意，`Kilometers`不是 \*\*一个独立的新类型 \*\*。具有 `Kilometers`类型的值将被视为与 `u64`类型的值相同：

```
    let x: u64 = 5;
    let y: Kilometers = 5;
    assert(x + y == 10);

```

Because `Kilometers` and `u64` are the same type, we can add values of both types and we can pass `Kilometers` values to functions that take `u64` parameters. However, using this method, we don’t get the type checking benefits that we get from introducing a *separate* new type called `Kilometers`. In other words, if we mix up `Kilometers` and `i32` values somewhere, the compiler will not give us an error.

因为`Kilometers`和`u64`是同一类型，我们就可以添加两种类型的值，我们可以将`Kilometers`的值传递给接受`u64`参数的函数。然而，使用这种方法，我们无法得到类型检查的好处，因为我们引入了一个名为 `Kilometers`的 *独立的* 新类型。换句话说，如果我们把`Kilometers`和`i32`的值混在一起，编译器不会给我们一个错误。

The main use case for type synonyms is to reduce repetition. For example, we might have a lengthy array type like this:

类型同义词的主要使用情况是减少重复。例如，我们可能有一个很长的数组类型，像这样：

```
[MyStruct<u64, b256>; 5]

```

Writing this lengthy type in function signatures and as type annotations all over the code can be tiresome and error prone. Imagine having a project full of code like this:

将这种冗长的类型写在函数签名中，并作为类型注释在代码中随处可见，会让人感到厌烦和容易出错。想象一下，有一个项目充满了这样的代码：

```
fn foo_long(array: [MyStruct<u64, b256>; 5]) -> [MyStruct<u64, b256>; 5] {
    array
}

```

A type alias makes this code more manageable by reducing the repetition. Below, we’ve introduced an alias named `MyArray` for the verbose type and can replace all uses of the type with the shorter alias `MyArray`:

类型别名通过减少重复而使这段代码更容易管理。下面，我们为冗长的类型引入了一个名为`MyArray`的别名，可以用更短的别名`MyArray`来代替该类型的所有应用：

```
fn foo_long(array: [MyStruct<u64, b256>; 5]) -> [MyStruct<u64, b256>; 5] {
    array
}

```

This code is much easier to read and write! Choosing a meaningful name for a type alias can help communicate your intent as well.

这段代码读起来和写起来都容易多了! 为类型别名选择一个有意义的名字，也有助于传达你的意图。