Zend PHP 7 Certification – OOP – Type Hinting

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

Type declarations, or type hints as they were previously known, are used to specify the expected data type of an argument in a function declaration.

Prior to PHP 7, you could use the following types.

  • Class/interface name
  • self
  • array
  • callable
  • Now, you can use scalar types.

    • bool – The parameter must be a boolean value
    • float – The parameter must be a floating point number
    • int – The parameter must be an integer
    • string – The parameter must be a string

    Here is a basic function expecting two arguments that are of the int data type.

    function sum(int $a, int $b) {
        return $a + $b;
    var_dump(sum(1, 2));
    // Outputs: int(3)

    If the given value is of the incorrect type, then an error is generated. In PHP 5, this will be a recoverable fatal error, while PHP 7 will throw an uncaught TypeError exception.

    You can catch a TypeError within a try-catch block.

    try {
        var_dump(sum('string1', new stdClass()));
    } catch (TypeError $e) {
        echo 'Error: '.$e->getMessage();

    The default behaviour of PHP is that it will try and coerce values of the wrong type into the expected scalar type if possible. If for example, a function that is given an integer for a parameter that expects a string will get a variable of type string.

    If strict mode is enabled (which can be done on a per-file basis), only a variable of exact type of the type declaration will be accepted, or a TypeError will be thrown. The only exception to this rule is that an integer may be given to a function expecting a float.

    Strict mode can be enabled by using the declare() construct.

    function sum(int $a, int $b) {
        return $a + $b;
    var_dump(sum('1', '2')); // TypeError thrown

    View the other sections:

    Note: This article is based on PHP version 7.0.