Collections

Draft provides three primary collection types: arrays, maps, and sets.

Arrays

Ordered, indexed collections of same-type elements.

Creating Arrays

@numbers: Array<Int> = [1, 2, 3, 4, 5]
@names: Array<String> = ["Alice", "Bob", "Charlie"]
@empty: Array<Float> = []

Array Literals

@list = [1, 2, 3]
@repeated = [0; 10]  @// Array of 10 zeros

Accessing Elements

@first = @list[0]       @// 1
@last = @list[@list#length - 1]  @// 3

Modifying Arrays

mut @list = [1, 2, 3]
@list[0] = 10           @// [10, 2, 3]
@list#push(4)           @// [10, 2, 3, 4]
@list#pop()             @// Returns 4, list is [10, 2, 3]
@list#insert(1, 99)     @// [10, 99, 2, 3]
@list#remove(1)         @// Removes element at index 1

Array Properties

@list#length    @// Number of elements
@list#is_empty  @// true if length == 0
@list#first     @// First element
@list#last      @// Last element

Array Methods

@list#slice(1, 3)       @// Sub-array from index 1 to 3
@list#reverse()         @// Reversed copy
@list#sort()            @// Sorted copy
@list#map(fn(@x) => @x * 2)      @// Transform each element
@list#filter(fn(@x) => @x > 2)   @// Keep matching elements
@list#reduce(0, fn(@acc, @x) => @acc + @x)  @// Sum all
@list#contains(3)       @// true if element exists
@list#index_of(3)       @// Index of first occurrence

Iterating Arrays

for @item in @list
    write(@item)
fin for.

for @index, @item in @list
    write(string(@index) + ": " + string(@item))
fin for.

Maps

Key-value pair collections.

Creating Maps

@scores: Map<String, Int> = {"Alice": 95, "Bob": 87}
@empty: Map<String, String> = {}

Accessing Values

@score = @scores["Alice"]     @// 95
@maybe = @scores#get("Dave")  @// Option<Int>

Modifying Maps

mut @scores = {"Alice": 95}
@scores["Bob"] = 87          @// Insert or update
@scores#insert("Charlie", 92) @// Insert
@scores#remove("Alice")       @// Remove key

Map Properties

@scores#length      @// Number of entries
@scores#is_empty    @// true if empty
@scores#keys        @// Array of keys
@scores#values      @// Array of values
@scores#contains("Alice")  @// true if key exists

Iterating Maps

for @key, @value in @scores
    write(@key + ": " + string(@value))
fin for.

Sets

Collections of unique elements.

Creating Sets

@unique: Set<Int> = {1, 2, 3, 4, 5}
@letters: Set<Char> = {'a', 'b', 'c'}

Set Operations

@a = {1, 2, 3}
@b = {2, 3, 4}

@a#union(@b)         @// {1, 2, 3, 4}
@a#intersection(@b)  @// {2, 3}
@a#difference(@b)    @// {1}
@symmetric_diff(@a, @b)  @// {1, 4}

Modifying Sets

mut @set = {1, 2, 3}
@set#add(4)           @// Add element
@set#remove(2)        @// Remove element
@set#contains(3)      @// true

Iterating Sets

for @item in @set
    write(@item)
fin for.

Performance Characteristics

Operation	Array	Map	Set
Access	O(1)	O(1)	O(1)
Insert	O(1)*	O(1)	O(1)
Remove	O(n)	O(1)	O(1)
Search	O(n)	O(1)	O(1)

*Amortized for push at end

Choosing a Collection

Use Case	Collection
Ordered list of items	Array
Fast lookup by key	Map
Unique items, membership test	Set
Stack (LIFO)	Array (push/pop)
Queue (FIFO)	Array (push/shift)

Next Steps

Continue to Strings for string manipulation.