Maps in Go

A map in Go is an unordered collection of key–value pairs.
It is similar to a dict in Python.

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Declaring Maps

// Declare without init (nil map, unusable until initialized)
var m map[string]int

// Declare and init with make
m = make(map[string]int)

// Shorthand (inside functions)
m := make(map[string]int)

// With literal values
m := map[string]int{
    "route": 66,
    "speed": 120,
}

Adding and Updating Values

m := make(map[string]int)

m["route"] = 66       // add new key
m["route"] = 100      // update existing key
m["speed"] = 120      // add another
fmt.Println(m)
// map[route:100 speed:120]

Checking if Key Exists

value, ok := m["route"]
if ok {
    fmt.Println("Found:", value)
} else {
    fmt.Println("Key not found")
}

Deleting Keys

delete(m, "route")

Passing Maps to functions

func addData(m map[string]int, key string, value int) {
    m[key] = value // modifies original map (reference type)
}

func main() {
    m := make(map[string]int)
    addData(m, "Route", 89)
    addData(m, "Highway", 24)
    fmt.Println(m)
    // map[Route:89 Highway:24]
}

Key Points

• Maps are reference types → passing to functions updates the original.
• Keys must be of a comparable type (string, int, bool, structs without slices/maps/functions).
• Maps are unordered → iteration order is random.
• A nil map can be compared, but not written to.