Go中的struct {}和struct {} {}如何工作? [英] How do struct{} and struct{}{} work in Go?

问题描述

我想知道Go中的"struct {}"和"struct {} {}"是什么意思?一个例子如下:

I am wondering what does "struct{}" and "struct{}{}" mean in Go? An example is as follows:

array[index] = struct{}{}

或

make(map[type]struct{})

推荐答案

struct是关键字在Go中.它用于定义结构类型，该结构类型是一系列命名元素.

struct is a keyword in Go. It is used to define struct types, which is a sequence of named elements.

例如:

type Person struct {
    Name string
    Age  int
}

struct{}是具有零个元素的struct类型.通常在不存储任何信息时使用.它具有大小为0的优点，因此通常不需要内存来存储类型为struct{}的值.

The struct{} is a struct type with zero elements. It is often used when no information is to be stored. It has the benefit of being 0-sized, so usually no memory is required to store a value of type struct{}.

struct{}{}是复合文字，它构造了一个类型的值struct{}.复合文字为诸如结构，数组，映射和切片之类的类型构造值.它的语法是大括号后跟元素的类型.由于空"结构(struct{})没有字段，因此元素列表也为空:

struct{}{} on the other hand is a composite literal, it constructs a value of type struct{}. A composite literal constructs values for types such as structs, arrays, maps and slices. Its syntax is the type followed by the elements in braces. Since the "empty" struct (struct{}) has no fields, the elements list is also empty:

 struct{}  {}
|  ^     | ^
  type     empty element list

作为示例，让我们在Go中创建一个集合". Go没有内置的集合数据结构，但是它具有内置的映射.我们可以将地图用作集合，因为一张地图最多只能有一个具有给定键的条目.并且由于我们只想在地图中存储键(元素)，因此我们可以选择地图值类型为struct{}.

As an example let's create a "set" in Go. Go does not have a builtin set data structure, but it has a builtin map. We can use a map as a set, as a map can only have at most one entry with a given key. And since we want to only store keys (elements) in the map, we may choose the map value type to be struct{}.

包含string元素的地图:

var set map[string]struct{}
// Initialize the set
set = make(map[string]struct{})

// Add some values to the set:
set["red"] = struct{}{}
set["blue"] = struct{}{}

// Check if a value is in the map:
_, ok := set["red"]
fmt.Println("Is red in the map?", ok)
_, ok = set["green"]
fmt.Println("Is green in the map?", ok)

输出(在转到操场上尝试):

Is red in the map? true
Is green in the map? false

请注意，但是，在地图外创建集合时，使用bool作为值类型可能更方便，因为检查元素中是否包含元素的语法更简单.有关详细信息，请参见如何创建包含唯一字符串的数组?.

Note that however it may be more convenient to use bool as the value type when creating a set out of a map, as the syntax to check if an element is in it is simpler. For details, see How can I create an array that contains unique strings?.

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