struct{} update

Author: 刘建秋

EN/struct/struct.md

@@ -26,4 +26,35 @@ This also confirms that many answers often go back to the roots of computer data
 
 For struct types, the order of the fields is critical. If two struct types contain exactly the same fields, but in a different order or are partially merged, then the two structs are different types!
 
-If the struct field starts with a capital letter, then the field is exported (visible outside the package), which also conforms to the visibility rules of the Go language. So a struct can contain both exported and unexported variables.
+If the struct field starts with a capital letter, then the field is exported (visible outside the package), which also conforms to the visibility rules of the Go language. So a struct can contain both exported and unexported variables.
+
+
+### struct{} empty structure
+
+* struct{} features
+struct{} is an element free structure type, which is usually used when there is no information storage. The advantage is that the size is 0 and no memory is needed to store values of type struct{}.
+* The difference between struct{} and struct{}{}
+Struct{}{} is a literal, which constructs a struct{} type value, which is also null.
+* Declare as map[string]struct{}
+Since struct{} is empty and does not care about the content, the map is transformed into set
+Map can obtain whether the key exists through the "comma OK" mechanism, for example_ , OK: = map ["key"], if there is no corresponding value, OK is false.
+* Chan struct{}
+can be used as exit of channel
+* Two structt{}{}} 
+addresses are equal
+
+```
+var set map[string]struct{}
+// Initialize the set
+set = make(map[string]struct{})
+// Add some values to the set:
+set["one"] = struct{}{}
+set["two"] = struct{}{}
+// Check if a value is in the map:
+A kind of , ok := set["one"]
+//output true
+fmt.Println ("Is one in the map?", ok)
+A kind of , ok = set["three"]
+//output  false
+fmt.Println ("Is three in the map?", ok)
+```

zh_CN/struct/struct.md

@@ -27,3 +27,37 @@ PHP就是c语言实现的一套高级“程序”语言，只不过是这套“
 对于struct类型来说，字段的先后顺序是非常关键的。如果两个struct类型包含了完全相同的字段，但是排列顺序不同或者进行了部分合并，那么这两个struct就是不同的类型！
 
 如果struct字段是大写字母开头，那么该字段就是导出的（包外可见），这也符合Go语言的可见性规则。因此一个struct可以同时包含导出和未导出的变量。
+
+### struct{} 空结构体
+
+* struct{} 特点
+struct{}是一个无元素的结构体类型，通常在没有信息存储时使用。优点是大小为0，不需要内存来存储struct {}类型的值。
+* struct{} 和 struct{}{} 区别
+struct{}{}是一个复合字面量(literal)，它构造了一个struct {}类型的值，该值也是空。
+* 声明为声明为map[string]struct{}
+由于struct{}是空，不关心内容，这样map便改造为set
+map可以通过“comma ok”机制来获取该key是否存在,例如_, ok := map["key"],如果没有对应的值,ok为false。
+* chan struct{}：可以用作通道的退出
+* 两个structt{}{}地址相等
+
+```
+var set map[string]struct{}
+// Initialize the set
+set = make(map[string]struct{})
+
+// Add some values to the set:
+set["one"] = struct{}{}
+set["two"] = struct{}{}
+
+// Check if a value is in the map:
+_, ok := set["one"]
+
+//output true
+fmt.Println("Is one in the map?", ok)
+_, ok = set["three"]
+
+//output  false
+fmt.Println("Is three in the map?", ok)
+```
+
+