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Amit Merchant

Amit Merchant

A blog on PHP, JavaScript, and more

Nullable types in PHP 7.1

Today, while reading through the code of laravel-vouchers package, I stumbled upon this litle code which looks like this.

 * @param string $prefix
public function setPrefix(?string $prefix): void
    $this->prefix = $prefix;

Noticed ?string type-hint in the function parameter? This is the thing that had got me. I wondered what this means and why it is useful. So, I needed to find it out. And after a little Googling, I found that these are called as Nullable types which are added in PHP 7.1.

What are Nullable types?

Nullable type simply means when you prepends ? to the type name while declaring types in the method parameters or for return values, it will be marked as nullable. This signifies that as well as the specified type, NULL can be passed as an argument, or returned as a value, respectively.

So, if you type hint parameter with ? like below

function printMe(?string $name)

printMe('FooBar'); // string(10) "FooBar"
printMe(null); // NULL

As you can see, the method will accept both string and null as a parameter without any error and process them likewise. But if you don’t pass any arguments it then it will result into a fatal error.

Similarly, if you type hint return type of a method with ? like below

function testReturn(): ?string
    return 'FooBar';

var_dump(testReturn()); // FooBar

function testReturn(): ?string
    return null;

var_dump(testReturn()); // NULL
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