How do you create optional arguments in php?

ghostz00_2687 0
Viewed 173233

In the PHP manual, to show the syntax for functions with optional parameters, they use brackets around each set of dependent optional parameter. For example, for the date() function, the manual reads:

string date ( string $format [, int $timestamp = time() ] )

Where $timestamp is an optional parameter, and when left blank it defaults to the time() function's return value.

How do you go about creating optional parameters like this when defining a custom function in PHP?

php
7 Answers

Much like the manual, use an equals (=) sign in your definition of the parameters:

function dosomething($var1, $var2, $var3 = 'somevalue'){
    // Rest of function here...
}
Jeff_Winkworth_13060

The default value of the argument must be a constant expression. It can't be a variable or a function call.

If you need this functionality however:

function foo($foo, $bar = false)
{
    if(!$bar)
    {
        $bar = $foo;
    }
}

Assuming $bar isn't expected to be a boolean of course.

Ross_20250

Some notes that I also found useful:

  • Keep your default values on the right side.

    function whatever($var1, $var2, $var3="constant", $var4="another")

  • The default value of the argument must be a constant expression. It can't be a variable or a function call.

ghostz00_26870

Give the optional argument a default value. 

function date ($format, $timestamp='') {
}
mk_17970

Starting with 7.1 there is a type hinting for nullable parameters

function func(?Object $object) {}

It will work for these cases:

func(null); //as nullable parameter
func(new Object());  // as parameter of declared  type

But for optional value signature should look like.

function func(Object $object = null) {} // In case of objects
function func(?Object $object = null) {} // or the same with nullable parameter

function func(string $object = '') {} // In case of scalar type - string, with string value as default value
function func(string $object = null) {} // In case of scalar type - string, with null as default value
function func(?string $object = '') {} // or the same with nullable parameter

function func(int $object = 0) {} // In case of scalar type - integer, with integer value as default value
function func(int $object = null) {} // In case of scalar type - integer, with null as default value
function func(?int $object = 0) {} // or the same with nullable parameter

than it can be invoked as  

func(); // as optional parameter
func(null); // as nullable parameter
func(new Object()); // as parameter of declared type
user_55548250
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