初始化地图问题

Question

我正在开发一个项目，我需要声明以下内容：

mapDataPayload := make(map[string][]*dataPayload)

如果我向它附加数据，它会正常工作。

mapDataPayload := make(map[string][]*dataPayload)

for {

    select {

    case rcvData := <-ch:

        mapDataPayload[rcvData.Topic] = append(

            mapDataPayload[rcvData.Topic],

            &dataPayload{Message: rcvData.Message},

        )

    }

}

但是，我想设置一个大小限制。随着追加，它会不停地增长。我想要实现的是当达到限制（最大值：100）时，它会覆盖索引 0、1、2 ...

mapDataPayload[rcvData.Topic][0]

mapDataPayload[rcvData.Topic][1]

我尝试用以下方法初始化以下内容：

make(map[string][]*dataPayload, 100)

for {

    select {

    case rcvData := <-ch:

        mapDataPayload[rcvData.Topic][0] = &dataPayload{Message: rcvData.Message}

    }

}

但是，如果我检查长度，它将返回 0。用直接初始化 (mapDataPayload[rcvData.Topic][0]) 替换 append 会立即导致错误。

所以，我想要做的是用一个限制填充 map[string][]*dataPayload，例如这个数据：

{

  "test1": {

    "0": {

      "Message": "Heasdllo"

    },

    "1": {

      "Message": "Hel132lo"

    },

    "2": {

      "Message": "Hedsallo"

    }

  },

  "testanother": {

    "0": {

      "Message": "adsad"

    },

    "1": {

      "Message": "Helwqe2lo"

    },

    "2": {

      "Message": "Hel21321lo"

    },

    "3": {

      "Message": "Hel21321lo"

    }

  }

}

当它达到数字 100 时，我想回到数字 0、1、2...

Answer 1

您可以像这样为循环缓冲区实现数据结构package mainimport (&nbsp; &nbsp; "fmt")type Circle struct&nbsp; {&nbsp; &nbsp;Size int&nbsp; &nbsp;Contents []interface{}&nbsp; &nbsp;Pointer int}func (c *Circle) Setup(n int) {&nbsp; &nbsp;(*c).Size=n&nbsp; &nbsp;(*c).Contents=make([]interface{},n)}func (c *Circle) Add(value interface{}) {&nbsp; &nbsp;(*c).Contents[(*c).Pointer] = value&nbsp; &nbsp;(*c).Pointer = ((*c).Pointer+1) % (*c).Size}func main() {&nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload := make(map[string]*Circle)&nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload["aaa"]=&Circle{}&nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload["aaa"].Setup(10)&nbsp; &nbsp; for i:=0; i<9999; i++ {&nbsp; &nbsp; &nbsp; mapDataPayload["aaa"].Add(i)&nbsp; &nbsp; }&nbsp; &nbsp; mapDataPayload["aaa"].Add("banana")&nbsp; &nbsp; fmt.Println(mapDataPayload["aaa"].Contents)}更新为使用 interface{} 以便可以使用任何类型的数据

Answer 2

像这样使用：for {&nbsp; &nbsp; select {&nbsp; &nbsp; case rcvData := <-ch:&nbsp; &nbsp; &nbsp; &nbsp; _, exists := mapDataPayload[rcvData.Topic]&nbsp; &nbsp; &nbsp; &nbsp; if !exists {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload[rcvData.Topic] = []*dataPayload{}&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; if len(mapDataPayload[rcvData.Topic]) < 100 {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload[rcvData.Topic] = append(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload[rcvData.Topic],&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &dataPayload{Message: rcvData.Message},&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; )&nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; mapDataPayload[rcvData.Topic][len(mapDataPayload[rcvData.Topic]) % 100] = &dataPayload{Message: rcvData.Message}&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}