Hack语言类型化简介

于typechecker的匹配下,Hack语言的类型化能力是Hack其他职能特色的基石。开发Hack语言的严重性思想也亏为代码提供显式类型标注以便对代码进行项目一致性与黑错误分析。
当下是用于比Hack特性的一个实例,用传统PHP形式编写:

<?php

namespace Hack\UserDocumentation\Types\Intro\Examples\PreHack;

class Z {}
class A {
  public $a;
  public $b;

  public function __construct($a, $b) {
    $this->a = $a;
    $this->b = $b;
  }

  public function foo($x, $y) {
    return $x * $this->a + $y * $this->b;
  }
}

function bar(A $a, $x, $y) {
  return $a->foo($x, $y);
}

function baz() {
  $a = new A(2, 4);
  $z = new Z();
  var_dump(bar($a, 9, 4));
  // Did we really want to allow passing a stringy int?
  var_dump(bar($a, 8, "3"));
  // Did we really want to allow passing booleans?
  var_dump(bar($a, true, false));
  // This will throw a fatal at runtime
  var_dump(bar($z, 1, 1));
}

baz();
Output
int(34)
int(28)
int(2)

Catchable fatal error: Argument 1 passed to Hack\UserDocumentation\Types\Intro\Examples\PreHack\bar() must be an instance of Hack\UserDocumentation\Types\Intro\Examples\PreHack\A, Hack\UserDocumentation\Types\Intro\Examples\PreHack\Z given in /data/users/joelm/user-documentation/guides/hack/20-types/01-introduction-examples/pre-hack.php on line 22

上述示范可以圆满运行于HHVM上(除了以结尾的var_dump处发生一个沉重错误)。尽管如此,在群者它并未明晰的发表有开发者的作用。比如,开发者是否允许A::foo()接受字符串类型的int值。当然,习惯及的处理方式,如经is_int()函数来检测或者抛出异常可以解决这种情况。

唯独若望下面的事例,开发者的意是否再度鲜明:

<?hh

namespace Hack\UserDocumentation\Types\Intro\Examples\Hack;

class Z {}
class A {
  public int $a;
  public int $b;

  public function __construct(int $a, int $b) {
    $this->a = $a;
    $this->b = $b;
  }

  public function foo(int $x, int $y): int {
    return $x * $this->a + $y * $this->b;
  }
}

function bar(A $a, int $x, int $y): int {
  return $a->foo($x, $y);
}

function baz(): void {
  $a = new A(2, 4);
  $z = new Z();
  var_dump(bar($a, 9, 4));
  // Did we really want to allow passing a stringy int? NO!
  // The typechecker will actually error here before you even run the program,
  // so you can catch problems before runtime.
  var_dump(bar($a, 8, "3"));

  // Did we really want to allow passing booleans? NO!
  // The typechecker will error here too.
  var_dump(bar($a, true, false));

  // This will throw a fatal at runtime
  // The typechecker will error here as well
  var_dump(bar($z, 1, 1));
}

baz();

/****

Type checker errors:

hack.php:29:23,25: Invalid argument (Typing[4110])
  hack.php:20:28,30: This is an int
  hack.php:29:23,25: It is incompatible with a string
hack.php:31:20,23: Invalid argument (Typing[4110])
  hack.php:20:20,22: This is an int
  hack.php:31:20,23: It is incompatible with a bool
hack.php:31:26,30: Invalid argument (Typing[4110])
  hack.php:20:28,30: This is an int
  hack.php:31:26,30: It is incompatible with a bool
hack.php:33:16,17: Invalid argument (Typing[4110])
  hack.php:20:14,14: This is an object of type
                     Hack\UserDocumentation\Types\Intro\Examples\Hack\A
  hack.php:26:8,14: It is incompatible with an object of type
                    Hack\UserDocumentation\Types\Intro\Examples\Hack\Z
*****/
Output
int(34)

Catchable fatal error: Argument 3 passed to Hack\UserDocumentation\Types\Intro\Examples\Hack\bar() must be an instance of int, string given in /data/users/joelm/user-documentation/guides/hack/20-types/01-introduction-examples/hack.php.type-errors on line 22

瞧是例子里之代码,我们好很清楚的知情就容传递int型值。这样API的调用者知道得传递什么类型的价。为艺术与总体性添加显式类型声明,配合Hack
typechecker,你不怕有矣平等舒缓真正的雅强之平安根基的动态编程语言。

倘惦记打听代码中得以应用什么项目及以啊纺织显式类型标注,查看:

  • 项目系统
  • 品种标注

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