Maps

A Map is a collection of key/value pairs.

A Map is like a List, but instead of having a numbered index (1, 2, 3), each item corresponds with (or “maps to”) a String key.

Maps are surrounded by curly braces { } and each key/value pair is joined by a colon :.

// An empty Map
$user = {}

// A one-line Map
$user = { name: 'Tashi', age: 33 }

// A multi-line Map
$user = {
    name: 'Tashi',
    job: 'Technologist',
    location: 'Tunisia',
    age: 33,
}

TipThink of a List as a collection of many things, while a Map usually holds the properties of a single thing. (It’s very common to have a List of Maps, such as a set of rows from a database query.)

JargonIn other languages, Maps are called many different things: associative arrays, dictionaries, hash maps, hashes, or records. They all basically mean the same thing: a set of key/value pairs.

Accessing Map Fields

Use dot (.) notation to set and get fields that are defined in the Map.

$user = {
    name: 'Tashi',
    age: 33,
}

$user.name
//= 'Tashi'

$user.email
//= ✕ ERROR - 'email' is not defined

Dynamic Map Values

Often, Maps are used to create an index with dynamic key/value pairs.

Use [] notation to safely set and get dynamic values.

$numBooks = {}

$numBooks['Anne Tyler'] = 23
$numBooks['Henry Thoreau'] = 17

$favoriteAuthor = 'Anne Tyler'
$numBooks[$favoriteAuthor]
//= 23

$numBooks['Nelson Nobody']
//= ''  (a safe falsey value)

Keyword Maps

If you omit a value of a Map property, it will automatically take the value of the key string itself.

$map = { xx, yy, zz }

// is the same as...

$map = {
    xx: 'xx',
    yy: 'yy',
    zz: 'zz',
}

You can use this to emulate an Enumerated Type (aka “Enum”) in other languages.

$alertLevel = { Red, Yellow, Green }

if $alert == $alertLevel.Red {
    print('- Wooop! Wooop! -')
}

Map Methods

Here are some common Map methods.

$calories = {
    taco: 400,
    taters: 300,
    tortellini: 500,
}

$calories.keys()
//= ['taco', 'taters', 'tortellini']

$calories.hasKey('taters')
//= true

See the Map class for all other methods.

Next: Loops