I'm trying to create a slice of Maps. Although the code compiles fine, I get the runtime error below:
mapassign1: runtime·panicstring("assignment to entry in nil map");
I attempt to make an array of Maps, with each Map containing two indicies, a "Id" and a "Investor". My code looks like this:
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
I initially thought something like below would work, however that did not fix the issue either. Any ideas?
invs := make([]make(map[string]string), length)
A map maps keys to values. The zero value of a map is nil . A nil map has no keys, nor can keys be added. The make function returns a map of the given type, initialized and ready for use.
Go Maps Zero value of a mapA nil map has no keys nor can keys be added. A nil map behaves like an empty map if read from but causes a runtime panic if written to. var m map[string]string // reading m["foo"] == "" // true.
Go by Example: Maps To create an empty map, use the builtin make : make(map[key-type]val-type) . Set key/value pairs using typical name[key] = val syntax. Printing a map with e.g. fmt. Println will show all of its key/value pairs.
You are trying to create a slice of maps; consider the following example:
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)
}
You can rewrite these lines:
invs[i] = make(map[string]string)
invs[i]["Id"] = inv_ids[i]
invs[i]["Investor"] = inv_names[i]
as:
invs[i] = map[string]string{"Id": inv_ids[i], "Investor": inv_names[i]}
this is called a composite literal.
Now, in a more idiomatic program, you'd most probably want to use a struct
to represent an investor:
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])
}
}
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