Maps

TBD.

Also known as Associative Arrays, or Objects in other languages.

All maps must have a definition, which define their fields and datatypes. There can also be anonymous maps, which may contain any key.

Named Maps

// Here we define a map, called Person
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map Person {
  String name,
  String surname,
  Int age,
}

// Here we declare an instance of a Person.
val john_doe = Person {
  name: "John",
  surname: "Doe",
  age: 33,
}

// If the compiler can infer the type of a Map,
// we can omit its type
var Person mary_jane = .{
  name: "Mary",
  surname: "Jane",
  age: 27,
}
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To access the fields of a map we use square braces [].

mary_jane["age"] += 1
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print(mary_jane["name"])  // Mary
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Or dot access . if the field’s name is a valid identifier.

mary_jane.age += 1
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print(mary_jane.name)
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Anonymous maps

An anonymous map allows us to store and retrieve any key of any datatype. They are declared as Map.

val car = Map {
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  brand: "Toyota",
  model: "Corolla",
  year: 2012,
}
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Anonymous maps can also can have their type omitted.

var car = .{
          ╰╴Invalid variable declaration
  brand: "Toyota",
  model: "Corolla",
  year: 2012,
}
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If the compiler encounters a map without a type (that is, .{}) and doesn’t expect a specific type, it will assume it is an anonymous map.

We can freely assign fields to an anonymous map:

// Modify an existing field
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car["year"] = 2015
// Create a new field
car["status"] = "used"
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However, if we try to access a field of an anonymous map we’ll get a nullable type, and we must annotate it.

// This is ok, we are declaring what datatype we expect
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String? car_status = car["status"]

// This won't work, the compiler doesn't know what datatype to use
var car_status = car["status"]
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Instead, we can use the get function of the map, which expects a datatype and returns that type as nullable

val car_status = car.get[String]("status")
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Both ways to get a value will check that the key exists in the map, and that it has the correct datatype. If either the key doesn’t exist or it has a different datatype, it will return null.

We can also use dynamic keys, following the same rules:

val generated_value = "key"
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String? v = map[generated_value]
// or
val v = map[String](generated_value)
thp