Map

The map data type in Filtrera is used to represent sequences of keyed values. This reference guide provides a detailed specification of the map data type, its syntax, and usage for users already familiar with the concept.

Type Notation for Maps

The type notation for maps is {<key type> -> <value type>}.

Example

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}

Defining Maps

Built-in Map (Dictionary)

The built-in Dictioanry is a Map that uses a hash mechanism to quickly lookup values based on provided keys.

Example

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}
from map->'key2'
// Returns 2

See Also

Records also implement the Map interface.

Runtime-provided Maps

Other Map implementations can be provided by the runtime.

Maps are Not Ordered

The Map interface doesn’t enforce any order of the keys, values or pair entries. Do not rely on values being returned in any certain order.

Maps as Iterators

All maps are also Iterators. When iterating a map, the values are returned.

Practical Usage

Example: Accessing an Item by Key

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}
from map->'key2'
// Returns 2

Example: Getting the Keys of a Map

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}
from map keys
// Returns ['key2', 'key1', 'key3']

Note that the order of the keys are undeterministic.

Example: Get Entries as an Iterator of Tuples

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}
from map entries
// Returns [('key2', 2), ('key1', 1), ('key3', 3)]

Example: Counting Items in an Map

let map: { text -> number } = {
  'key1' -> 1
  'key2' -> 2
  'key3' -> 3
}
from map count

Summary

The map data type in Filtrera represents a map between keys and values. Built-in maps, referred to as dictioanries, can be defined using curly brackets, while other maps can be provided by the runtime. Maps can be used as iterators of it’s values. By understanding its syntax and usage, including defining maps, accessing values, and using filters and functions such as keys and entries, you can leverage maps to create expressive and functional programs. The ability to handle runtime-provided maps further enhances the flexibility and robustness of your Filtrera programs.