is it possible to have a function inside a defined constant?

Question

According to https://www.tutorialspoint.com/php/php_constants.htm a normal costant is define by using define() function plus a value:

define('TEST', 123);

I think it would be interesting and useful if there were a way to define a constant with a function inside:

define ('ME', function($test){
   if($test == true){
       return "Whats up";
   }else{
       return "whats down";
   }
});

Then perhaps I could do something like this?

 if($I_Said === ME($val)){
     do something;
 }

Is there a such a way to do this?

No, it's [not possible](http://php.net/manual/en/function.define.php). It's would be an awful way of defining global functions anyway. — Mike Doe, Sep 21 '18 at 10:52
Possible duplicate of [How to define global functions in PHP](https://stackoverflow.com/questions/4458837/how-to-define-global-functions-in-php) — Philipp Maurer, Sep 21 '18 at 10:53
If this was possible, a big downside would be that functions and constants would now have an overlapping namespace. If I say `define ('echo', function() { ... })` then PHP wouldn't know if I wanted to run the native `echo` or my new defined function. It would be a breaking-change to any code that defined a constant with the same name as an internal function. — iainn, Sep 21 '18 at 11:00
Different lookup tables. Once the interpreter encounters `FOO()` it will only search the function declaration list. It won't even consider `define("FOO", "BAR");` for overrides. — mario, Sep 21 '18 at 11:04

score 3 · Answer 1 · answered Sep 21 '18 at 10:53

3

There's no syntactical or other important difference on the caller side to:

function ME() {}

if ($I_Said === ME($val))

So, just do that.

answered Sep 21 '18 at 10:53

deceze

1

Yeah i know this is possible. I was just wondering if my question was possible – LukeDS Sep 21 '18 at 10:55
1

What would be the advantage if it was? – deceze Sep 21 '18 at 10:55
1

dont know, perhaps none. But would be nice to learn if there was one. Just to understand what PHP is capable of doing really. – LukeDS Sep 21 '18 at 10:58
1

And no, there are technical reasons against it. The interpreter needs to know whether `ME()` refers to a function or a constant which should be executed as a function, which is quite a big deal, and the current solution is that it simply can never refer to a constant. – deceze Sep 21 '18 at 10:59

1 Answers1