# 4.4.4-4 内置复合类型

除了基础类型之外，Go 语言规范中还定义了多种复合类型，编译器为每种类型都定义了对应的数据结构

## 4.4.4-4.1. 数组

数组类型（Array）的结构定义如下：

```go
type Array struct {
    len  int64
    elem Type
}
```

数组是定长的数据容器，所以除了元素类型之外，数组长度也是其类型中的组成部分，因此`[2]int`与`[3]int`虽然都是整型数组，但对类型系统而言，他们属于不同的类型。

## 4.4.4-4.2. 切片

切片类型（Slice）的结构定义如下：

```go
type Slice struct {
    elem Type
}
```

切片是变长的数据容器，其类型定义中不包括长度信息。

## 4.4.4-4.3. Map

Map 类型的结构定义如下：

```go
type Map struct {
    key, elem Type
}
```

其中`key`必须是可比较的数据类型（Comparable Type），后文中[类型的比较规则](/golang-bian-yi-qi-lei-xing-jian-cha/4.4.413-lei-xing-de-bi-jiao-gui-ze.md)有详细介绍。

## 4.4.4-4.4. Channel

Channel 类型的结构定义如下：

```go
type Chan struct {
    dir  ChanDir
    elem Type
}

// A ChanDir value indicates a channel direction.
type ChanDir int

// The direction of a channel is indicated by one of these constants.
const (
    SendRecv ChanDir = iota
    SendOnly
    RecvOnly
)
```

其中一个是 channel 的元素类型，一个是 channel 的数据流方向。

## 4.4.4-4.5. 指针

指针类型的结构定义如下：

```go
type Pointer struct {
    base Type // element type
}
```


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