Why You Can't Take the Address of a Map Value in Go

You cannot take the address of a map value because map lookups return a copy of the value, not a reference to the stored data. To modify a map value in place, you must store the address of the value in the map itself by using a pointer type as the map's value type.

m := make(map[string]*int)
val := 42
m["key"] = &val
*m["key"] = 100 // Modifies the value in place

If you need to modify a value retrieved from a map with a non-pointer type, you must reassign it back to the map.

m := make(map[string]int)
m["key"] = 42
m["key"] = m["key"] + 100 // Reassigns the updated copy

In Go, accessing a value from a map gives you a temporary copy, not the actual data stored in memory. Because this copy exists only for that moment, you cannot get its memory address or change it directly. Think of it like photocopying a document; you can't change the original file by writing on the photocopy. To fix this, store pointers in the map or reassign the updated copy back to the map key.