What are "union types" and how do you use them in PHP?
In this shot, I want you to learn about a PHP feature called “union type” and how to implement or use it both in PHP 7 and PHP 8. Without any further ado, let’s get started.
What is a union type?
Generally speaking, union types are defined as follows:
A collection of values stored within the same position in memory with different data types/formats.
In short, union type allows you to define a collection of two or more types (int, float…) for your variables or function parameters. For example, you can have a function in your program that accepts a parameter of the int or string type.
The union type’s typical syntax looks like this:
public function foo(Foo|Bar $input): int|float;
The foo function (above) accepts a parameter, ＄input, of type both Foo and Bar, and returns a value of either an int or float.
Union type in PHP 7
PHP 7 only supports these two special union types:
- Nullable union types using the
?Typenotation:public function bar(?Bar ＄bar): void; ArrayorTraversableusing the iterable type
PHP 7 does not support arbitrary union types, but as a workaround, we can use phpdoc annotation. Let’s see an example of its use below:
<?phpclass Student{/*** @var int|float $roomNo*/private $roomNo;/*** @param int|float $roomNo*/public function setRoomNo($roomNo) {$this->roomNo = $roomNo;}/*** @return int|float*/public function getRoomNo() {return $this->roomNo;}}$newStudent1 = new Student;$newStudent1->setRoomNo(25.0);$newStudent2 = new Student;$newStudent2->setRoomNo(4);echo "Student 1 number is " .$newStudent1->getRoomNo(). "<br>";echo "Student 2 number is " .$newStudent2->getRoomNo();
Now, let’s look at how “union type” is improved in PHP 8.
Union type in PHP 8
As we’ve seen above, PHP 7 lacks built-in support for arbitrary union types. So, PHP 8 has implemented built-in support for arbitrary union types.
With the same example as above, here’s how you can make use of union types in PHP 8:
<?phpclass Student{private int|float $roomNo;public function setRoomNo(int|float $roomNo): void {$this->roomNo;}public function getRoomNo(): int|float {return $this->roomNo;}}$newStudent1 = new Student;$newStudent1->setRoomNo(25.0);$newStudent2 = new Student;$newStudent2->setRoomNo(4);echo "Student 1 number is " .$newStudent1->getRoomNo(). "<br>";echo "Student 2 number is " .$newStudent2->getRoomNo();
Note
- the
voidtype can never be part of a union type because it indicates that the function does return any value- nullable union type can also be written as:
public function foo(Foo|null ＄foo): void;
Conclusion
Union types are a great functionality in PHP that let us define a variable of multiple types in our program. PHP 7 supports arbitrary union types through phpdoc annotation, whereas PHP 8 has built-in support for it.
