8. Collections and Text

This chapter covers the containers and text tools used in everyday TalkTalk programs: arrays, ranges, loops, strings, and dictionaries.

Arrays

[T] is a growable, copy-on-write array:

let numbers = [10, 20, 30]
numbers.push(40)
print(numbers[1])
numbers[0] = 99
print(numbers.count)

Common operations include get, push, pop, swap, and indexed access. get returns an optional; subscript syntax is the direct form.

[T; N] is an InlineArray whose static length is part of the type. Use it for fixed-size data and static value generic APIs.

Iteration

for uses Iterable and Iterator. Iterator adapters are lazy until collected:

let result = [1, 2, 3, 4].map { $0 * 10 }.skip(count: 1).to_array()

print(result)

A user type can participate by conforming to Iterator:

struct Countdown {
	let remaining: Int
}

extend Countdown: Iterator {
	mut func next() -> Int? {
		if self.remaining == 0 { return .none }
		self.remaining = self.remaining - 1
		return .some(self.remaining + 1)
	}
}

for number in Countdown(remaining: 3) {
	print(number)
}

for x in consume values consumes the source. for x in mut values iterates with writeback.

Ranges

lower..<upper excludes the upper bound and lower..upper includes it:

for i in 0..<3 {
	print(i) // 0, 1, 2
}
for i in 1..3 {
	print(i) // 1, 2, 3
}

Integer ranges conform to Iterable without allocating an array.

Unicode text

Strings are UTF-8, and their user-facing character operations use extended grapheme clusters:

print("héllo 👋🏽".count())
print("héllo 👋🏽".utf8().count())
print("👨‍👩‍👧‍👦".count())

Iterating a String or Substring produces Character values. Lower-level views are explicit:

• .utf8() iterates encoded bytes
• .scalars() iterates Unicode scalar values
• ordinary iteration produces grapheme-cluster Character values

The text surface includes searching, splitting, trimming, replacement, Unicode classification, case conversion, normalization, and cursor/index APIs. Index types carry provenance so an index from unrelated text cannot silently address a different string.

String building and conversion

StringBuilder supports repeated construction without a chain of intermediate strings. String and Substring implement StringMethods; many operations therefore read naturally as methods on either owned text or a view.

Showable converts values for display through .show(), and print accepts any Showable value. From<Source> and Into<Target> describe general library conversions.

Dictionaries

The standard library's dict module provides a growable string-keyed Dict<Value>:

use dict::{ Dict }

let scores = Dict<Int>()
scores.insert(key: "ada", value: 100)

match scores.get(key: "ada") {
	.some(score) -> print(score),
	.none -> print("missing")
}

The standard library is still growing; consult the source modules for the complete current API.