PHP closures require arguments passed

Question

Trying to figure out why php anonymous functions only work when they are given parameters in the function header.

For example

$f = function(){
    echo "hello world";
};
$f;
$f();

won't work. But

$f = function($argument){
    echo $argument;
}
$f('hello world');

works just fine.

Why does it need arguments and is there any work around for this?

EDIT

This must be a version issue. I'm on 5.3.18 and my first example definitely doesn't work. For those not believing, it throws:

Parse error: syntax error, unexpected T_FUNCTION in index.php(192) : 
  eval()'d code on line 1

EDIT

After looking at DaveRandom's answer I'm back to having no idea what's happening. That is if they are correct that it works in 5.3.10 ...

nickb · Accepted Answer · 2012-06-22 01:00:32Z

5

This is perfectly valid syntax and outputs hello world:

$f = function(){
    echo "hello world";
};
$f();

The line $f; does nothing, and would be equivalent to declaring any other variable and then writing that new variable name and a semicolon.

Anonymous functions do not require parameters, see the manual for more details about them.

You are getting those syntax errors because you are running a PHP version < 5.3.

edited Jun 22, 2012 at 1:00

answered Jun 22, 2012 at 0:25

nickb

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5 Comments

nickb Over a year ago

@DanielNill - Are you sure you're running PHP > 5.3? See my edit - Your errors are conducive of a mismatch.

Daniel Nill Over a year ago

It would seem so. php -version gives

PHP 5.3.8 with Suhosin-Patch (cli) (built: Nov 15 2011 15:33:15) Copyright (c) 1997-2011 The PHP Group Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies

. But it must be a configuration issue or that the php version on my command line does not match the version on my xampp install. Closures were introduced in 5.3 so I would think that if they work with an argument in a given version they would work without arguments in that same version...

nickb Over a year ago

That might not be the case: php -version from the command line can invoke a different PHP than what's being executed on the server. Do echo phpversion(); in a PHP script and load that in your browser to see.

Daniel Nill Over a year ago

Yeah looks like it was a version issue. upgrading php seems to have fixed it. Wonder why passing an argument to the function worked...

DaveRandom Over a year ago

@DanielNill I can find no record of this as a bug or feature change, since 5.3.8 or otherwise. May be a bug with suhosin? Maybe you had some other syntax error in your test case? It seems like you have now fixed this so it is now academic, but out of interest what error were you getting? E_PARSE or some kind of run-time error?

mario · Accepted Answer · 2012-06-22 00:27:06Z

4

This doesn't invoke the closure:

$f;

But this one does:

$f();

Function calls require parens to be recognized by the parser. If you just mention the variable $f; then that's an empty expression. The closure object contained in $f gets assigned to a temporary zval (variable placeholder), then thrown away.

answered Jun 22, 2012 at 0:27

mario

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Comments

DaveRandom · Accepted Answer · 2012-06-22 00:32:35Z

3

The first code works fine if you remove the meaningless $f; line.

Edit Actually, it still works even if you leave that line in. And in 5.3.10 as well.

edited Jun 22, 2012 at 0:32

answered Jun 22, 2012 at 0:26

DaveRandom

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6 Comments

nickb Over a year ago

It's only working in your example because of the $f();, if you remove that, it doesn't print anything.

DaveRandom Over a year ago

@nickb Well yes, it you never call it it won't do anything... but surely that's a given?

nickb Over a year ago

I suppose I don't understand what you mean by "it works both ways" then. Which ways are you referring to?

Ruan Mendes Over a year ago

@nickb whether you have the the useless statement $f in there or not

DaveRandom Over a year ago

@nickb I thought that $f; on a line on it's own would throw an error, but apparently not. I just meant that you can leave the line in and it still works (it's more obvious if you check the codepads). I'll edit to make it clearer.

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