Return type hints

Type hinting features are not limited to function parameters only; as of PHP 7, they expand to function return values as well. The same rules that apply to function parameters hinting, apply to function return type hinting. To specify a function return type, we simply follow the parameter list with a colon and the return type, as shown in the following example:

function register(string $user, int $age) : bool {
  // logic ...
  return true;
}

Developers can still write functions with multiple conditioned return statements; its just that in this case, each of these return statements, when reached, will have to match the hinted return type, otherwise \TypeError will be thrown.

The function return type hints play nicely with super types. Let's take a look at the following example:

class A {}
class B extends A {}
class C extends B {}

function getInstance(string $type) : A {
    if ($type == 'A') {
       return new A();
       } elseif ($type == 'B') {
           return new B();
       } else {
           return new C();
       }
  }

getInstance('A'); #object(A)#1 (0) { }
getInstance('B'); #object(B)#1 (0) { }
getInstance('XYZ'); #object(C)#1 (0) { }

We see that the function executes nicely for all three types. Given that B extends A directly, and C extends B, the function accepts them as the return value.

Given the dynamic nature of PHP, function return types might seem like a step in the wrong direction at first, more so because a lot of PHP code out there already uses the PHPDoc @return annotation, which plays nicely with modern IDE tools, such as PhpStorm. However, the @return annotation is merely informative, it does not enforce an actual return type during runtime, and it really makes sense only with a powerful IDE. Using the function return type hints ensures that our functions return what we intended them to return. They do not stand in the way of PHP's dynamic nature; they merely enrich it from a function consumer point of use.