Required parameter $xxx follows optional parameter $yyy

Question

Deprecated: Required parameter $xxx follows optional parameter $yyy in...

Since upgrading to PHP 8.0 this error is thrown when running code like this:

function test_function(int $var1 = 2, int $var2) {
    return $var1 / $var2;
}

This has worked in past versions of PHP without issue.

Solution 1

This style of function declaration has been deprecated in PHP 8.0. Writing functions like this has never made sense, since all parameters (up to the last required one) would need to be specified when the function was called. It also caused confusion with use of the ReflectionFunctionAbstract class to analyze functions and methods.

The new deprecation simply ensures that function signatures follow the common sense assumption that required parameters, which must appear, should always be declared before optional ones.

The function should be rewritten to remove the default value on the earlier parameters. Since the function could never be called without declaring all parameters, this should have no effect on its functionality.

function test_function(int $var1, int $var2) {
    return $var1 / $var2;
}

Solution 2

The required parameter without a default value should come first.

function test_function(int $xxx, int $yyy = 2)
{
    return $xxx * $yyy;
}
 

Comments

[Darren Murphy]

Change the order of the parameters, placing $xxx ahead of the optional parameter $yyy.

[miken32]

There is an answer to the question already. Doing what you suggest would mean rewriting every use of your function across your code base.

[Rain]

"since all parameters (up to the last required one) would need to be specified when the function was called" . I disagree 3v4l.org/Nb6i6 ;)

[miken32]

Very impressive nitpicking! 👍🏼

[Enverex]

"Writing functions like this has never made sense" - I disagree. There are often occasions where arguments may be ordered differently for sanity or readability reasons. This deprecation seems like an unnecessary and annoying change.

[miken32]

@Enverex the default value specified in such a case could never be used, so it serves no purpose. I've been programming professionally in PHP for more than 15 years and I've never needed to do it. Argument order and default values are not intended for use as documentation, that's what PHPDoc is for.

[Enverex]

"the default value specified in such a case could never be used" Yes it could, you pass null for values you wish to use the default. Also I'm not talking documentation here, just friendlier argument ordering.

[miken32]

@Enverex If you pass null you get null for the parameter, not the default value. 3v4l.org/MGWIR

[miken32]

And then update every usage of that method throughout your code?

[Alemoh Rapheal Baja]

I don't think you'll have to do so except it throws an error.

[chiliNUT]

@Rain what php8 feature is your example using? Assuming it must be a new php8 feature since its a syntax error in the previous versions.

[Rain]

@chiliNUT Named Arguments.

[Alemoh Rapheal Baja]

the parameter that is required without a default value should come first

[Ray Perea]

@Rain - I disagree too. My 2 cents... This PHP8 deprecation wasn't well thought out at all. In PHP8, they added named parameters which means that you can now call parameters in any order as long as you call them by name like this: func(param1: "value1", param2: "value2") So, that syntax compliments being able to specify default values for any parameter in any order. @miken32 - You said "since all parameters (up to the last required one) would need to be specified when the function was called" - This isn't true anymore

[miken32]

Every place you use that method you would need to change your code. Why would you do this instead of just setting a default on the second parameter?

[Omkar Ghurye]

@miken32 "If a parameter with a default value is followed by a required parameter, the default value has no effect." This is deprecated as of PHP 8.0.0 and can generally be resolved by dropping the default value or by changing the position of parameters as suggested above, without a change in functionality.

[miken32]

It completely changes the function; now you have to find and rewrite every single line of code that uses this function. My question was, why is this better than just dropping the default value, which involves no changes to other code? Not to mention this subpar approach has already been given in another answer.