Is it possible to write strictly typed PHP code?

Question

For example, is it possible to write code like this:

int $x = 6;
str $y = "hello world";
bool $z = false;
MyObject $foo = new MyObject();

And is it possible to define functions like this:

public int function getBalance()
{
   return 555; //Or any numeric value
}

Answer 1

In PHP 7 are implemented "Scalar Type Declarations", e.g.:

public function getBalance(): int {
    return 555;
}

You need to declare, that you will use strict types:

<?php
    declare(strict_types=1);

    function sum(int $a, int $b): int {
        return $a + $b;
    }

    sum(1, 2);
?>

More information: https://wiki.php.net/rfc/scalar_type_hints_v5

Answer 2

Edit: This answer applies to versions of PHP 5.6 and earlier. As noted in recent answers, PHP version 7.0 and later does have some support for this

---

Original answer:

No. There is only support for type hinting since php5, but "Type Hints can only be of the object and array (since PHP 5.1) type. Traditional type hinting with int and string isn't supported."

In PHP 7 are implemented "Scalar Type Declarations" see the answer below.

That is as far as php currently goes, and as far as it should go if you ask me.

Answer 3

PHP is not strictly typed, so no. That said, it does support limited type hinting on functions - that's as close as it gets.

Answer 4

Unfortunately NO! I am at the end of a big project now that involves a lot alogorithms (graph theory, circuits etc) and I wish I hadn't choose php.

I have been using php for about 10 years, and still believe it is a good language, however one have to decide! What is bad for me, lack of strict typing might be good for someone else.

In addition, I want to mention, that I often wrote extra code for supporting strict typing, just a plain example is this:

if (is_array($r) && count($r)===0)

and the errors and hidden situations etc that were revealed are beyond explanation.

There were mistakes and situations that I would never been able to think/detect apriori, writing all these extra code was not enjoying but at least it will save me from silly mistakes!

If I would go back, maybe I would chose php for the web part, you know getting and showing data to the user, php is just great for that, handling string, arrays, talking to the database etc etc, but for the main core, algorithms etc I would go for C++, maybe haskell.. don't know, at least something strictly typed.

Answer 5

Something you might try in order to simulate a poor man's strict type checking is using assert() to force the output to be of a particular type before you return it:

/**
 * Get Balance
 *
 * @return int
 */
function getBalance()
{
    /* blah blah blah */
   $out = 555; //Or any numeric value
   assert('is_int($out)');
   return $out;
}

So you keep your assertions active all throughout development and testing, sort of like the checks the compiler does at compile-time.

Granted, the assert() page is keen to assert that you shouldn't use assertions to check input parameters, but rather use normal conditionals to check them.

This answer had what I thought was a good rule:

The rule of thumb which is applicable across most languages (all that I vaguely know) is that an assert is used to assert that a condition is always true whereas an if is appropriate if it is conceivable that it will sometimes fail.

If you're simulating strict type-checking (writing your code to viciously maintain types; not trying to validate input from the outside), then you ought to be certain what the type is unless you've made a mistake.

Update:

There's also this: http://hacklang.org/ Facebook's PHP-based language with static typing.

Answer 6

Perhaps you should try this PHP extension https://github.com/krakjoe/strict. Support for the following types is introduced:

• string
• integer, int
• float, double
• boolean, bool
• resource

Answer 7

You could use h2tp transpiler to transpile HACK code to PHP:

You can do this thanks to Facebook Team and HACK Language.

Visit http://hacklang.org and http://hhvm.com for more info.

If you want to code directly in Hack + HHVM environment you can also use Facebook's internal IDE Nuclide

Answer 8

Since the answer is basically "no", an alternative: A PHP "linter", which should catch some of the things a compile-time check would catch in a staticly-typed language like C. Not the same, but should prevent some sillyness

"Is there a static code analyzer [like Lint] for PHP files" lists many of these.

Answer 9

PHP 7.0 introduced function return type hints, and PHP 7.4 added support for class property type hints. As of PHP 7.4, your code would be:

<?php declare(strict_types=1);

class MyObject
{
}

class TypedStuff
{
  public static int $x;
  public static string $y;
  public static bool $z;
  public static MyObject $foo;
}

function getBalance(): float
{
  return 555; //Or any numeric value
}

TypedStuff::$x = 6;
TypedStuff::$y = "hello world";
TypedStuff::$z = false;
TypedStuff::$foo = new MyObject();

You can't type-hint one-off variables, but you can type-hint static class properties, which could be used in an almost identical manner. You can also type-hint the return type of stand-alone functions.

More commonly, you'd be defining typed values inside a class using a typed setter, and receiving typed values outside a class using a typed getter, like:

<?php declare(strict_types=1);

class Person {
  private $age;

  public function __construct(int $age)
  {
    $this->age = $age;
  }

  public function setAge(int $age): void { $this->age = $age; }
  public function getAge(): int { return $this->age; }
}

$person = new Person(30);
echo sprintf(
  'The person is %d years old.',
  $person->getAge()
);

This works in PHP 7.0 because property type-hints are not required.

Answer 10

No. That syntax will not work.

You could, theoretically, come up with a system of objects that enforced their own sort of strict typing, but it wouldn't perform and ...why would you want to, anyway?

If you need strict typing, use a strictly typed language.