Zend PHP 7 Certification – Functions – Type Declarations

This post covers the Type Declarations section of the Functions chapter when studying for the Zend PHP 7 Certification.

You can use type declarations to specify the expected data type of an argument in a function declaration. In PHP 5.5, these were the allowed types introduced.

  • Class/interface name
  • self
  • array
  • callable
class C {}
class D extends C {}

// This doesn't extend C.
class E {}

function f(C $c) {
    echo get_class($c)."\n";

f(new C);
f(new D);
f(new E);

// Outputs:

Fatal error: Uncaught TypeError: Argument 1 passed to f() must be an instance of C, instance of E given

As of PHP 7.0, support for scalar types such as string, bool, int and float were introduced.

To specify a type declaration, the type name should be added before the parameter name. The declaration can be made to accept NULL values if the default value of the parameter is set to NULL.

function test(bool $param) {



By default, type declarations are in coercive mode. This means that if the type of the argument is not the expected type, PHP will try and correct it.

In strict mode, if a scalar type is not the expected type, a TypeError will be thrown. The only exception to this rule is that an integer may be given to a function expecting a float.

To declare strict mode, use the declare keyword specifying the strict type.


function addNumbers(int $num1, int $num2) {
    return $num1 + $num2;

var_dump(addNumbers(1, 2)); // Outputs: int(3)
var_dump(addNumbers(1, 2.5)); // Fatal error

View the other sections:

Note: This article is based on PHP version 7.1.