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5c226704d5
Reverting back to `php` as the `hack` header is likely not supported and the `php` highlighting is probably good enough (for now) to at least render the page.
421 lines
12 KiB
Markdown
421 lines
12 KiB
Markdown
---
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language: Hack
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contributors:
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- ["Andrew DiMola", "https://github.com/AndrewDiMola"]
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- ["Stephen Holdaway", "https://github.com/stecman"]
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- ["David Lima", "https://github.com/davelima"]
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filename: learnhack.hh
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---
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[Hack](https://hacklang.org/) lets you write code quickly, while also having safety features built in, like static typechecking.
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To run Hack code, [install HHVM](https://docs.hhvm.com/hhvm/installation/introduction), the open-source virtual machine.
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```php
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/* ==================================
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* READ THE DOCS!
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* ==================================
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*/
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/* For more information on the Hack language:
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* - About Hack: https://hacklang.org/
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* - Documentation: https://docs.hhvm.com/hack/
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*/
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/* ==================================
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* A NOTE ON PHP
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* ==================================
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*/
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// The Hack language began as a superset of PHP.
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// Since then, the languages have (largely) diverged.
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// You may encounter the .php extension, which is no longer recommended.
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/* ==================================
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* COMMENTS
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* ==================================
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*/
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// Hack has single-line comments...
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/* Multi-line comments...
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*
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*/
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/**
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* ... and a special syntax for doc comments.
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*
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* Use doc comments to summarize the purpose of a definition, function, class or method.
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*/
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/* ==================================
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* NAMESPACES
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* ==================================
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*/
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// Namespaces contain definitions of classes, interfaces, traits, functions, and constants.
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namespace LearnHackinYMinutes {
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/* ==================================
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* TYPES
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* ==================================
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*/
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function demo_hack_types(): void {
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// Hack has five primitive types: bool, int, float, string, and null.
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$is_helpful = true; // bool
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$int_value = 10; // int
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$precise_value = 2.0; // float
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$hello_world = "Hello World!"; // string
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$null_string = null; // null
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// Create a `shape` with the shape keyword, with a series of field names and values.
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$my_point = shape('x' => -3, 'y' => 6, 'visible' => true);
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// Create a `tuple` with the tuple keyword, with a series of two or more types as values.
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$apple_basket = tuple("apples", 25); // different types are OK
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// Use `arraykey` to represent either an integer or string.
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$the_answer = 42;
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$is_answer = process_key($the_answer);
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// Similarly, `num` represents either an int or float.
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$lucky_number = 7;
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$lucky_square = calculate_square($lucky_number);
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}
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function process_key(arraykey $the_answer): bool {
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if ($the_answer is int) {
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return true;
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} else {
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return false;
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} // true
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}
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function calculate_square(num $arg)[]: float {
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return ((float)$arg * $arg);
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}
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// Enums are limited to int or string (as an Arraykey), or other enum values.
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enum Permission: string {
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Read = 'R';
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Write = 'W';
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Execute = 'E';
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Delete = 'D';
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}
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// In contrast, an enum class can be of any value type!
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enum class Random: mixed {
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int X = 42;
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string S = 'foo';
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}
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/* ==================================
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* HACK ARRAYS
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* ==================================
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*/
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// The following line lets us use functions in the `C\` namespace.
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use namespace HH\Lib\C; // the `C` library operates on containers
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function demo_hack_arrays(): void {
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// vec: ordered
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$v = vec[1, 2, 3];
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$letters = vec['a', 'b', 'c'];
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$letters[0]; // returns 'a'
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$letters[] = 'd'; // appends 'd'
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// `inout` provides pass-by-reference behavior
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C\pop_back(inout $letters); // removes 'd'
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C\pop_front(inout $letters); // removes 'a'
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// keyset: ordered, without duplicates
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$k = keyset[1, 2, 3]; // values must be int or string
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$colors = keyset['red', 'blue', 'green'];
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// keyset keys are identical to their values
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$colors['blue']; // returns 'blue'.
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$colors[] = 'yellow'; // appends 'yellow'
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unset($colors['red']); // removes 'red'
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// dict: ordered, by key-value
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$d = dict['a' => 1, 'b' => 3]; // keys must be int or string
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$alphabet = dict['a' => 1, 'b' => 2];
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$alphabet['a']; // indexing at 'a' returns `1`
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$alphabet['c'] = 3; // adds a new key-value pair of `c => 3`
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unset($alphabet['b']); // removes 'b'
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}
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/* ==================================
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* THE HACK STANDARD LIBRARY (HSL)
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* ==================================
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*/
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// The Hack Standard Library is a set of functions and classes for the Hack language.
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// Namespace use declarations are ideally at the top of your file but are placed here for instruction purposes.
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use namespace HH\Lib\Str; // The `Str` library operates on strings
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function demo_hack_standard_library(): void {
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$letters = vec['a', 'b', 'c'];
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$colors = keyset['red', 'blue', 'green'];
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$alphabet = dict['a' => 1, 'b' => 2];
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C\contains($letters, 'c'); // checks for a value; returns 'true'
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C\contains($colors, 'purple'); // checks for a value; returns 'false'
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C\contains_key($alphabet, 'a'); // checks for a key; returns 'true'
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C\contains($alphabet, 'd'); // checks for a value; returns 'false'
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Str\length("foo"); // returns `3`
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Str\join(vec['foo', 'bar', 'baz'], '!'); // returns `foo!bar!baz`
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}
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/* ==================================
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* HELLO WORLD!
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* ==================================
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*/
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use namespace HH\Lib\IO; // the `IO` library is a standard API for input / output
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<<__EntryPoint>> // required attribute for the typical entry/main function
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async function main(): Awaitable<
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void,
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> { // does not need to be named 'main' / is an asynchronous function
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await IO\request_output()->writeAllAsync(
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"Hello World!\n",
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); // prints 'Hello World'!
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}
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/* ==================================
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* FUNCTIONS
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* ==================================
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*/
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// Functions are defined globally.
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// When a function is defined in a class, we refer to the function as a method.
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// Functions have return types (here: `int`) and must return a value of
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// that type or return no value when a void return type annotation was used.
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function add_one(int $x): int {
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return $x + 1;
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}
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// Functions can also have defined, default values.
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function add_value(int $x, int $y = 1): int {
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return $x + $y;
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}
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// Functions can be variadic (unspecified length of arguments).
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function sum_ints(int $val, int ...$vals): int {
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$result = $val;
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foreach ($vals as $v) {
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$result += $v;
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}
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return $result;
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}
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// Functions can also be anonymous (defined with the `==>` arrow).
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// $f = (int $x): int ==> $x + 1;
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/* ==================================
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* PIPE OPERATOR
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* ==================================
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*/
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// The pipe operator, `|>`, evaluates the result of a left-hand expression
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// and stores the result in `$$`, the predefined pipe variable.
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use namespace HH\Lib\Vec;
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function demo_pipe_operator(): void {
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Vec\sort(Vec\map(vec[2, 1, 3], $a ==> $a * $a)); // vec[1,4,9]
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// the same result, but using the pipe operator and pipe variable:
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$x = vec[2, 1, 3]
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|> Vec\map($$, $a ==> $a * $a) // $$ with value vec[2,1,3]
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|> Vec\sort($$); // $$ with value vec[4,1,9]
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}
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/* ==================================
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* ATTRIBUTES
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* ==================================
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*/
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// Hack provides built-in attributes that can change runtime or static type checking behavior.
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// For example, we used the `__EntryPoint` attribute earlier in the "Hello World!" example.
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// As another example, `__Memoize` caches the result of a function.
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<<__Memoize>>
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async function do_expensive_task(): Awaitable<string> {
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$site_contents = await \HH\Asio\curl_exec("http://hacklang.org");
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return $site_contents;
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}
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/* ==================================
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* CONTEXTS
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* ==================================
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*/
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// Hack functions are attached to different contexts and capabilities.
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// A context is a grouping of capabilities; that is, a grouping of permissions.
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// To declare allowed contexts (and capabilities), use the Context List `[]`.
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// If contexts are not defined, your function includes permissions defined in Hack's `defaults` context.
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// Because the context list is NOT defined, the `defaults` context is implicitly declared.
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async function implicit_defaults_context(): Awaitable<void> {
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await IO\request_output()->writeAllAsync(
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"Hello World!\n",
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); // prints 'Hello World'!
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}
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// In the function below, the context list is defined to have the `defaults` context.
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// A function can have multiple contexts [context1, context2, ...].
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// `defaults` includes most of the capabilities defined by the Hack language.
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async function explicit_defaults_context()[defaults]: Awaitable<void> {
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await IO\request_output()->writeAllAsync("Hello World!\n");
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}
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// You can also specify zero contexts to create a pure function (no capabilities).
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async function empty_context()[]: Awaitable<void> {
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// The following line is an error, as the function does not have IO capabilities.
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// await IO\request_output()->writeAllAsync("Hello World!\n");
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}
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/* ==================================
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* GENERICS
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* ==================================
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*/
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// Generics allow classes or methods to be parameterized to any set of types.
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// That's pretty cool!
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// Hack typically passes by value: use `inout` to pass by reference.
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function swap<T>(inout T $input1, inout T $input2): void {
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$temp = $input1;
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$input1 = $input2;
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$input2 = $temp;
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}
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/* ==================================
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* CLASSES
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* ==================================
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*/
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// Classes provide a way to group functionality and state together.
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// To define a class, use the `class` keyword. To instantiate, use `new`.
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// Like other languages, you can use `$this` to refer to the current instance.
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class Counter {
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private int $i = 0;
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public function increment(): void {
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$this->i += 1;
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}
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public function get(): int {
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return $this->i;
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}
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}
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// Properties and Methods can be static (not requiring instantiation).
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class Person {
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public static function favoriteProgrammingLanguage(): string {
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return "Hack";
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}
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}
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function demo_hack_classes(): void {
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// Use `new` to instantiate a class.
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$c1 = new Counter();
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// To call a static property or method, use `::`
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$typical_person = tuple("Andrew", Person::favoriteProgrammingLanguage());
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}
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// Abstract class can be defined, but not instantiated directly.
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abstract class Machine {
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public function openDoors(): void {
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return;
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}
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public function closeDoors(): void {
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return;
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}
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}
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/* ==================================
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* INTERFACES
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* ==================================
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*/
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// A class can implement a set of requirements via an interface.
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// An interface is a set of method declarations and constants.
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interface Plane {
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// A constant is a named value. Once defined, the value cannot be changed.
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const MAX_SPEED = 300;
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public function fly(): void;
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}
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/* ==================================
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* TRAITS
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* ==================================
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*/
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// A trait defines properties and method declarations.
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// Traits are recommended when abstracting code for reuse.
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// Traits are included in code via the `use` keyword.
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trait Airplane {
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// Introduce a class or interface requirement with the following syntax:
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require extends Machine; // abstract class
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require implements Plane; // interface
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public function takeOff(): void {
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$this->openDoors();
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$this->closeDoors();
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$this->fly();
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}
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}
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class Spaceship extends Machine implements Plane {
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use Airplane;
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public function fly(): void {
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// fly like the wind
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}
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}
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/* ==================================
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* KEEP READING!
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* ==================================
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*/
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/* This is a simplified guide!
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* There's much more to learn, including:
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* - Asynchronous Operations: https://docs.hhvm.com/hack/asynchronous-operations/introduction
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* - Reified Generics: https://docs.hhvm.com/hack/reified-generics/reified-generics
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* - XHP: https://docs.hhvm.com/hack/XHP/setup
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* - ... and more!
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*/
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}
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```
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## More Information
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Visit the [Hack language reference](http://docs.hhvm.com/hack/) to learn more about the Hack language.
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For more information on HHVM, including installation instructions, visit the [official HHVM website](http://hhvm.com/).
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