运行时错误：“在无位图中进行赋值”

Question

我正在尝试创建一片地图。虽然代码编译好，我得到以下运行时错误：

mapassign1: runtime·panicstring("assignment to entry in nil map"); 

我试图做地图的数组，其中包含两个indicies，一个“身份证”和“投资者”每个地图。我的代码如下所示：

for _, row := range rows { 
     var inv_ids []string 
     var inv_names []string 

     //create arrays of data from MySQLs GROUP_CONCAT function 
     inv_ids = strings.Split(row.Str(10), ",") 
     inv_names = strings.Split(row.Str(11), ",") 
     length := len(inv_ids); 

     invs := make([]map[string]string, length) 

     //build map of ids => names 
     for i := 0; i < length; i++ { 
      invs[i] = make(map[string]string) 
      invs[i]["Id"] = inv_ids[i] 
      invs[i]["Investor"] = inv_names[i] 
     }//for 

     //build Message and return 
     msg := InfoMessage{row.Int(0), row.Int(1), row.Str(2), row.Int(3), row.Str(4), row.Float(5), row.Float(6), row.Str(7), row.Str(8), row.Int(9), invs} 
     return(msg) 
    } //for 

我最初认为类似下面会的工作，但它还是不解决问题。有任何想法吗？

invs := make([]make(map[string]string), length) 

Answer 1

您正在尝试创建地图的片;请看下面的例子：

http://play.golang.org/p/gChfTgtmN-

package main 

import "fmt" 

func main() { 
    a := make([]map[string]int, 100) 
    for i := 0; i < 100; i++ { 
     a[i] = map[string]int{"id": i, "investor": i} 
    } 
    fmt.Println(a) 
} 

可以重写这些行：

invs[i] = make(map[string]string) 
invs[i]["Id"] = inv_ids[i] 
invs[i]["Investor"] = inv_names[i] 

为：

invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]} 

这就是所谓的复合字面。

现在，一个更地道的程序，你最有可能想用一个struct来代表投资者：

http://play.golang.org/p/vppK6y-c8g

package main 

import (
    "fmt" 
    "strconv" 
) 

type Investor struct { 
    Id int 
    Name string 
} 

func main() { 
    a := make([]Investor, 100) 
    for i := 0; i < 100; i++ { 
     a[i] = Investor{Id: i, Name: "John" + strconv.Itoa(i)} 
     fmt.Printf("%#v\n", a[i]) 
    } 
}