rand

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Random data for Dart. Numbers, text, names, dates, networking, CSS colors, cryptographic tokens. One static class, two RNGs, all six platforms.

Rand.fullName();       // → 'Emma Rodriguez'
Rand.email();          // → 'olivia42@example.com'
Rand.ipv4();           // → '203.0.113.42'
Rand.password();       // → 'k9#Mx!pL2@qR'
Rand.color();          // → CssColors.coral
Rand.dateTime();       // → 2024-03-15 14:32:07.000Z
Rand.sample(from: ['rare', 'common'], count: 10, weights: [1, 100]);

What it's for

  • Test fixtures and seed data.
  • Mocking API responses.
  • Demos, prototypes, throwaway tokens.
  • Game prototyping (loot-box weighting, dice, color palettes).

What it isn't

  • Not faker. rand returns flat values. Compose typed entities yourself: User(name: Rand.fullName(), city: Rand.city()).
  • Not a crypto library. Rand.password() and Rand.nonce() use the platform CSPRNG, but the package's stability contract is "test data," not production secrets. Defaults may shift across major versions.
  • Not a UUID library. Rand.nonce() is opaque base62, not RFC 4122.

For composing structured fixtures (User, Address, Order, paginated responses, chat history) on top of these primitives, see example/recipes.dart.

Install

dart pub add rand

import 'package:rand/rand.dart';

Pure Dart. Works on android, ios, linux, macos, web, windows. No Flutter dependency.

Configuring the RNG

Rand.useRng(Random(42));      // any Random instance
Rand.seed(42);                // shortcut for useRng(Random(42))
Rand.useRng(Random.secure()); // cryptographically secure for non-crypto methods

useRng and seed mutate the global non-cryptographic RNG. Cryptographic methods (password, nonce, bytes, secureCharCode) always use Random.secure() and ignore both.

In parallel tests, set the RNG in setUp, not setUpAll — the global is shared.

Numbers

Rand.integer();                    // 0 to 2^31-1, inclusive both ends
Rand.integer(min: 50, max: 100);
Rand.float();                      // 0.0 to double.maxFinite, half-open
Rand.float(min: 0, max: 1);        // [0.0, 1.0)
Rand.boolean();                    // 50% true
Rand.boolean(90);                  // 90% true
Rand.latitude();                   // -90..90, 5 decimal places
Rand.longitude(3);                 // -180..180, 3 decimal places
Rand.charCode();                   // base62 code point (int)

integer(max: list.length) is inclusive — it can return list.length (out of bounds for indexing). Use max: list.length - 1, or just call Rand.element(list).

Networking

Rand.email();                       // 'olivia42@example.com'
Rand.email(domain: 'mycompany.io'); // 'james7@mycompany.io'
Rand.ipv4();                        // '203.0.113.42'
Rand.ipv6();                        // '2001:0db8:85a3:0000:0000:8a2e:0370:7334'
Rand.mac();                         // '3a:5f:9c:8e:2d:71'
Rand.mac(separator: '-');           // '3a-5f-9c-8e-2d-71'
Rand.hex(length: 40);               // git-SHA-shaped opaque hex
Rand.semver();                      // '3.7.42'
Rand.otp();                         // '047215'
Rand.slug();                        // 'lorem-ipsum-dolor'

email defaults pick from a built-in list of RFC 2606 example/test TLDs — safe to ship in fixtures without collision risk. ipv4 is not filtered for reserved ranges; compose your own filter if you need only routable addresses. ipv6 is returned in full form (no :: collapse) so fixture length stays stable. hex is general-purpose lowercase hex — git SHAs, ETags, opaque content hashes. semver, otp, slug use the non-secure RNG and are reproducible under Rand.seed.

Cryptographic — secure vs non-secure

Rand.bytes(32);              // Uint8List, always Random.secure()
Rand.nonce();                // 16-char base62, always Random.secure()
Rand.nonce(length: 32);
Rand.password();             // 12-char mixed-charset, always Random.secure()
Rand.password(length: 20, symbols: false);
Rand.base64();               // 16 bytes encoded, always Random.secure()
Rand.secureCharCode();       // base62 code point, always Random.secure()

Three rules:

  1. Seed doesn't reach secure methods. Rand.seed(42); Rand.password() is fresh CSPRNG output every call. For reproducible token tests, generate them from your own Random instance.
  2. Don't ship rand-generated tokens as production secrets. The RNG is correct; the package contract is "test data." Defaults can shift across major versions. Use package:cryptography or your platform's keystore for real secrets.
  3. bytes() and nonce() are always secure post-v4 — the secure: parameter is gone.

Identity & geo

Rand.firstName();   // 'Olivia'
Rand.lastName();    // 'Thompson'
Rand.fullName();    // 'James Michael Wilson' — 0..2 weighted middle names
Rand.alias();       // 'ShadowHunter'
Rand.city();        // 'Tokyo'
Rand.geoPoint();    // (lat: 42.36011, lng: -71.05891) — named record

Corpora are US/English-leaning. For locale-aware data, reach for package:faker.

Text — lorem corpus

Rand.word();                       // 'lorem'
Rand.words(count: 5);              // 'amet consectetur adipiscing elit sed'
Rand.words(count: 3, separator: '-');
Rand.sentence();                   // 'Lorem ipsum dolor sit amet.'
Rand.paragraph(3);                 // 3 sentences joined by '. '
Rand.article(5);                   // 5 paragraphs separated by '\n\n'

words(count: N) uses subSet — same word never repeats in one call. For repeats, call word() N times yourself.

Time

Rand.dateTime();                                       // 1970-01-01..2038-01-19 UTC
Rand.dateTime(DateTime(2020), DateTime(2025));         // custom range, half-open
Rand.duration(max: const Duration(days: 30));          // 0 to 30 days
Rand.duration(min: const Duration(days: 1), max: const Duration(days: 30));

dateTime and duration are [min, max) half-open.

Collections

enum Status { active, suspended, deleted }
final fruits = ['apple', 'orange', 'lemon', 'grape', 'kiwi'];
final scores = {'Alice': 95, 'Bob': 87};

Rand.element(fruits);              // 'orange'
Rand.enumValue(Status.values);     // Status.suspended — typed enum draw
Rand.subSet({1, 2, 3, 4, 5}, 3);   // {2, 5, 1} — unique elements
Rand.shuffled(fruits);             // ['kiwi', 'grape', 'apple', ...] — copy
Rand.mapKey(scores);               // 'Bob'
Rand.mapValue(scores);             // 95
Rand.mapEntry(scores);             // MapEntry('Alice', 95)

Pick the right call:

Need Use
One element element(iterable)
One enum member enumValue(MyEnum.values)
N unique elements subSet(set, N)
N elements, repeats okay sample(from: list, count: N)
N elements with weighted frequency sample(..., weights: [...])
Whole list, reordered shuffled(list)
One key / value / entry of a Map mapKey / mapValue / mapEntry

subSet requires Set<T> — dedupe explicitly with .toSet() if your source has duplicates.

Sampling — weighted draws with replacement

// Loot box: legendary 1%, rare 10%, common ~90%
final loot = Rand.sample(
  from: ['Legendary', 'Rare', 'Common'],
  count: 100,
  weights: [1, 10, 100],
);

// Equal probability — drop weights
final dice = Rand.sample(from: [1, 2, 3, 4, 5, 6], count: 10);

weights.length must be >= from.length. For a secure sample call Rand.useRng(Random.secure()) first.

Colors

final c = Rand.color();
c.name;     // 'coral'
c.argb;     // 0xFFFF7F50 — ARGB packed int
c.isDark;   // computed via CssColorsX extension (YIQ luminance)

Rand.colorDark();   // dark colors only — good for light backgrounds
Rand.colorLight();  // light colors only — good for dark backgrounds

148 CSS named variants. The argb int is Flutter-friendly: Color(c.argb) works without conversion. isDark is a CssColorsX extension getter — computed from argb via the YIQ luminance formula, not stored on the enum. Use it (or your own contrast helper, e.g. fluiver's Color.contrastText) to pick a foreground.

Probability helpers

Rand.boolean();             // 50% true
Rand.boolean(99.9);         // 99.9% true
Rand.nullable('value');     // 50% null, useful in fixtures
Rand.nullable('value', 90); // 90% null

Pitfalls

❌ ✅
Rand.integer(max: list.length) — inclusive, can return list.length Rand.element(list) or Rand.integer(max: list.length - 1)
Rand.seed(42); Rand.password() — seed never reaches CSPRNG Build deterministic tokens from your own Random(42)
Rand.subSet([1, 2, 2], 2) — list literal, duplicates collapse Pass a Set<T>: Rand.subSet({1, 2}, 2)
Rand.nullable(x, 80) thinking "80% present" Arg is nullChance — 80% returns null. Flip to Rand.nullable(x, 20) for 80% present
Shipping Rand.nonce / Rand.password as production secrets Use package:cryptography or a platform keystore
setUpAll(() => Rand.seed(42)) for parallel tests Use setUp — the global RNG is shared
list..shuffle() to "get a random order" without keeping the original Rand.shuffled(list) — non-mutating copy

License

MIT.

Libraries

rand
Random data generator for Dart.