Union types in practice in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a union type in PHP?

A union type allows a function or method to accept multiple different types for a parameter or return value, separated by a pipe (|). For example, int|string means the value can be either an integer or a string.

beginner

How do you declare a function parameter that accepts either an int or a string in PHP?

You declare it using a union type like this: <code>function example(int|string $param) { ... }</code>. This means <code>$param</code> can be an integer or a string.

intermediate

Can union types include null in PHP? How?

Yes, you can include null in union types by adding it explicitly, for example: int|string|null. This means the value can be an integer, a string, or null.

intermediate

What happens if a value passed to a union typed parameter does not match any of the allowed types?

PHP will throw a TypeError at runtime, indicating the value does not match the declared union types.

beginner

Show an example of a function with a union return type in PHP.

Example:<br><code>function getId(): int|string {<br>  return rand(0,1) ? 123 : 'abc';<br>}</code><br>This function returns either an integer or a string.

Which of the following is a valid union type declaration for a parameter that accepts int or string?

A function foo(int|string& $param) {}

B function foo(int&string $param) {}

C function foo(int|string $param) {}

D function foo(int|string, $param) {}

Union types use the pipe (|) symbol between types, so int|string is correct.

What will happen if you pass a float to a parameter declared as int|string?

A It will be accepted without error.

B PHP will throw a TypeError at runtime.

C PHP will convert the float to int automatically.

D The function will return null.

Only int or string are allowed. Passing a float causes a TypeError.

How do you include null as an allowed type in a union type?

A Use <code>int|string|null</code>

B Use <code>int|string?null</code>

C Use <code>int|string|void</code>

D Use <code>int|string|nullable</code>

You explicitly add null to the union types.

Can union types be used for return types in PHP?

A Only for class types.

B No, union types only work for parameters.

C Only for void return types.

D Yes, you can declare multiple return types using union types.

Union types can be used for both parameters and return types.

Which PHP version introduced union types?

A PHP 8.0

B PHP 8.1

C PHP 7.4

D PHP 8.2

Union types were introduced in PHP 8.0.

Explain what union types are and how you use them in PHP function parameters.

Think about allowing more than one type for a parameter.

Describe how PHP handles a value passed to a union typed parameter that does not match any allowed type.

What happens if the type is wrong?