How to Use a Map with Struct Keys in Go

You cannot use a struct as a map key directly because structs are not comparable by default in Go. To use a struct as a key, you must ensure all its fields are comparable types (like strings, ints, or pointers) or implement a custom hashing mechanism using the maphash package. For simple cases, just define the struct with comparable fields:

type Point struct {
    X int
    Y int
}

m := make(map[Point]string)
m[Point{1, 2}] = "A"

If your struct contains slices or maps, you cannot use it as a key; you must replace those fields with comparable types or use a string representation of the struct as the key instead.

Go map keys must be unique and comparable, meaning the language needs to be able to check if two keys are equal. Structs work as keys only if every field inside them is also comparable, like numbers or strings. Think of it like a library card: if the card has a photo that changes every time you look at it (like a slice), the library can't reliably find your book, so you can't use that card as an ID.