How Do Nullable Types Work in PHP7 and Beyond?

Nullable Types in PHP7: Understanding the Question Marks

PHP7 introduced the concept of nullable types, signified by the question mark (?) before a type declaration (?string, ?int). These types allow for a value to be either the specified type or null.

Parameters

When marking a parameter as nullable, it means that the function can accept either the specified type or null as an argument. For example:

public function (?string $parameter1, string $parameter2) {}

In this case, the function can receive either a string or null for $parameter1, but $parameter2 must be a string.

Return Type

Nullable types can also be used for return values. This indicates that the function can return either the specified type or null. For instance:

function error_func(): int {
    return null; // Invalid in PHP7.1+
}

function valid_func(): ?int {
    return null; // Valid in PHP7.1+
}

Property Type (PHP7.4 )

PHP7.4 introduced nullable types for property declarations. This allows a property to be either the specified type or null.

Nullable Union Types (PHP8 )

In PHP8, nullable types are shorthand for the union of the specified type and null. For example:

private ?object $bar = null; // PHP7.1+
private object|null $baz = null; // PHP8+

Error Handling

In PHP7.0 and earlier, using the question mark before a type declaration will result in a syntax error. PHP7.1 versions will accept nullable types.

References

• [Nullable Types](https://www.php.net/manual/en/language.types.declarations.php#language.types.declarations.nullable)
• [Class Properties Type Declarations](https://www.php.net/manual/en/language.oop5.properties.php#language.oop5.properties.declare)
• [Nullable Union Type](https://wiki.php.net/rfc/union_types_v2)

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