Nullable types in functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does a nullable type mean in PHP function parameters?

A nullable type means the function parameter can accept either the specified type or null. It is declared by adding a question mark ? before the type.

beginner

How do you declare a nullable integer parameter in a PHP function?

You declare it by adding a question mark before the type like this: <code>function example(?int $number) { ... }</code>. This means <code>$number</code> can be an integer or <code>null</code>.

intermediate

What happens if you pass null to a function parameter that is not nullable?

PHP will throw a TypeError because the parameter expects a specific type and null is not allowed unless the type is nullable.

intermediate

Can return types in PHP functions be nullable? How?

Yes, return types can be nullable by adding a question mark before the return type. For example: <code>function getValue(): ?string { ... }</code> means the function returns a string or <code>null</code>.

beginner

Why are nullable types useful in PHP functions?

Nullable types allow functions to explicitly accept or return null values, making the code clearer and safer by defining when null is an acceptable value.

How do you declare a nullable string parameter in a PHP function?

A function example(string? $param) {}

B function example(?string $param) {}

C function example(string|null $param) {}

D function example($param: ?string) {}

The correct syntax is to put a question mark before the type: ?string.

What will happen if you pass null to a non-nullable int parameter?

A PHP will throw a TypeError.

B It will work fine.

C The parameter will be converted to 0.

D PHP will ignore the parameter.

Passing null to a non-nullable parameter causes a TypeError in PHP.

Which of these is a valid nullable return type declaration?

A function foo(): array|null {}

B function foo(): array? {}

C function foo(): ?array {}

D function foo(): nullable array {}

The correct syntax for nullable return types is a question mark before the type, like ?array.

Nullable types were introduced in which PHP version?

A PHP 5.6

B PHP 7.4

C PHP 8.0

D PHP 7.1

Nullable types were introduced in PHP 7.1.

What does this function signature mean? function test(?float $value): ?float

A Parameter and return value can be float or null.

B Parameter must be float, return can be null.

C Parameter can be null, return must be float.

D Neither parameter nor return can be null.

Both the parameter and return type are nullable float, meaning they can be float or null.

Explain how to declare a nullable parameter and a nullable return type in a PHP function.

Think about the question mark symbol and where it goes.

Why is it important to use nullable types in PHP functions? Give an example scenario.

Consider when a value might be missing or optional.