Why Can't I Declare a Map as a Constant and Modify It in Go?

Declaring and Modifying Maps as Constants

In Go, maps are not constants, which means their key-value pairs cannot be modified after creation. Attempting to declare a map as a constant and subsequently fill it, as demonstrated in the snippet below, will result in an error:

const (
    paths = &map[string]*map[string]string{
        "Smith": {
            "theFather": "John",
        },
    }
    paths["Smith"]["theSon"] = paths["Smith"]["theFather"] + " Junior"
)

Reason

Constants represent immutable values, and the map type in Go does not allow for key-value pair modifications. The Spec restricts constant declarations to specific types, including boolean, rune, integer, floating-point, complex, and string constants.

Workaround

To resolve this issue, declare the map as a variable instead of a constant, as shown below:

var paths = map[string]*map[string]string{
    "Smith": {
        "theFather": "John",
    },
}
paths["Smith"]["theSon"] = paths["Smith"]["theFather"] + " Junior"

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