Hack

/***************************************************/
/****************** Hack Tutorial ******************/
/***************************************************/



/************ Click 'Next' to get started! *********/

<?php

// ^-- FIXME: replace <?php with <?hh

// A Hack file always starts with <?hh

<?hh

// Hack functions are annotated with types.

function my_negation(bool $x): bool {

  return !$x;

}

// FIXME: annotate this function parameter

// and return with the type 'int'.

function add_one(/* TODO */ $x): /* TODO */ {

  return $x+1;

}

<?hh

/* Hack errors come in multiple parts.

 * Hover over the underlined parts!

 */

function add_one(int $x): int {

  return $x+1;

}

function test(): void {

  $my_string = 'hello';

  // Some clever code ...

  add_one($my_string);

}

<?hh

// Prefixing a type with '?' permits null.

// TODO: fix the type of the parameter $x to permit null.

function f(int $x): void {

  var_dump($x);

}

function test(): void {

  f(123);

  f(null);

}

<?hh

interface User { public function getName(): string; }

function get_user_name(?User $user): string {

  if($user !== null) {

    // We checked that $user was not null.

    // Its type is now 'User'.

    /* TODO: return $user->getName() */

  }

  return '<invalid name>';

}

function test(User $user) {

  $name1 = get_user_name($user);

  $name2 = get_user_name(null);

}

<?hh

interface User { public function getName(): string; }

// There are many ways to handle null values.

// Throwing an exception is one of them.

function get_user_name(?User $user): string {

  if($user === null) {

    throw new RuntimeException('Invalid user name');

  }

  /* TODO: return $user->getName() */

}

function test(User $user) {

  $name1 = get_user_name($user);

  $name2 = get_user_name(null);

}

<?hh

// Hack introduces new collection types (Vector, Set and Map).

function test(): int {

  // Vector is preferred over array(1, 2, 3)

  $vector = Vector {1, 2, 3};

  $sum = 0;

  foreach ($vector as $val) {

    $sum += $val;

  }

  return $sum;

}

<?hh

// Hack uses generics for Collection types.

// TODO: fix the return type of the function 'test'

function test(): Vector<string> {

  $vector = Vector {1, 2, 3};

  return $vector;

}

<?hh

function vector_add1(Vector<int> $v): Vector<int> {

  // Example of lambda expressions.

  return $v->map($x ==> $x + 1);

}

function vector_mult2(Vector<int> $v): Vector<int> {

  // TODO: write a function multiplying all the elements by 2

}

/*

 * Congratulations!

 * You completed the beginner's tutorial.

 *