Maps

Maps are ordered key-value dictionaries. Keys are always stored as strings; values can be any type. Insertion order is preserved.

Literal Syntax

let user = {
    name: "Alice",
    age: 30,
    active: true
}

Bare identifiers (name:) are treated as string keys. String literals can also be used:

let config = {
    "host": "localhost",
    "port": 8080
}

An empty map is {}.

Reading Values

Bracket notation (dynamic key):

let name = user["name"]    // "Alice"

Dot notation (static key — must be a valid identifier):

let age = user.age         // 30

A missing bracket key returns null. A missing dot key raises a Type Error. Dot names such as length and keys resolve to built-in properties or methods first; use brackets to read keys with those names.

Writing Values

user["city"] = "Nairobi"   // bracket notation
user["score"] = 100         // use brackets for assignment

Key Membership

The in operator checks whether a key exists in a map:

if "name" in user {
    print("name is set")
}

if "email" not in user {
    print("no email on file")
}

Map Methods

See §15 Map Methods for the full method reference.

Maps and len()

let m = {a: 1, b: 2, c: 3}
print(len(m))   // 3