How to reset value in map of maps-CodePudding

Here's my code

{
    saruman := map[string]int{
     "power": 150,
     "skills": 200,
     "knowledge": 380,
    }

    gandalf := map[string]int{
     "power": 180,
     "skills": 210,
     "knowledge": 240,
    }

    wizards := make(map[string]interface{})
    wizards["saruman"] = saruman
    wizards["gandalf"] = gandalf

    fmt.Println(wizards)
    //OK map[gandalf:map[knowledge:240 power:180 skills:210] saruman:map[knowledge:380 power:150 skills:200]]

    //change gandalf property
    wizards["gandalf"]["knowledge"] = 310

    fmt.Println(wizards)
}

In the last line, we get:

NOK invalid operation: wizards["gandalf"]["knowledge"] (type interface {} does not support indexing)

CodePudding user response：

You cannot use ["key"] to access a structure that golang does not know about. Because it is an interface{} the value behind gandalf could be anything.

    wizards["gandalf"] = map[string]int{
         "knowledge": 310,
    }

You have to specify the type of data you are interacting with.

Playground: https://goplay.tools/snippet/O62ara8JbUv

CodePudding user response：

Need to cast it.

{
    saruman := map[string]int{
        "power":     150,
        "skills":    200,
        "knowledge": 380,
    }

    gandalf := map[string]int{
        "power":     180,
        "skills":    210,
        "knowledge": 240,
    }

    wizards := make(map[string]interface{})
    wizards["saruman"] = saruman
    wizards["gandalf"] = gandalf

    fmt.Println(wizards)
    //OK map[gandalf:map[knowledge:240 power:180 skills:210] saruman:map[knowledge:380 power:150 skills:200]]

    //change gandalf property
    wizards["gandalf"].(map[string]int)["knowledge"] = 10
    fmt.Println(wizards)
}

CodePudding user response：

This is the easier way:
one line code

wizards["gandalf"].(map[string]int)["knowledge"] = 110

Full example:

saruman := map[string]int{
    "power":     150,
    "skills":    200,
    "knowledge": 380,
}
gandalf := map[string]int{
    "power":     180,
    "skills":    210,
    "knowledge": 240,
}

wizards := make(map[string]interface{})
wizards["saruman"] = saruman
wizards["gandalf"] = gandalf

// fmt.Println(wizards)
// OK map[gandalf:map[knowledge:240 power:180 skills:210] saruman:map[knowledge:380 power:150 skills:200]]

// change gandalf property

wizards["gandalf"].(map[string]int)["knowledge"] = 110
fmt.Println(wizards["gandalf"].(map[string]int)["knowledge"])