Something I found interesting

Bonesnap

I've been looking at my code for the forum I created and decided I wanted to reorganize all my includes and whatnot into a much simpler system. I started fiddling around with things and noticed this:

test();

function test()
{
	echo 'The quick brown fox jumps over the lazy dog.';
}

This executes without issue as one would expect; even though the function was defined after it was used, there were no errors and the script behaved properly. Keeping on that same train of thought, I tried this:

echo TEST;

define('TEST', 'foobar');

And it produced a notice telling me the constant TEST was not defined. I find it interesting that in PHP you can use a function before its definition but not a constant. A quick peruse through the manual didn't mention why or anything related. I was under the impression the entire script is "compiled" or interpreted before executing, hence why something like a parse error can be detected if it's buried deep within a script.

Does anyone know why PHP behaves this way? I imagine there's a logical reason I guess I just don't know it. I'm using PHP 5.4.5 by the way.

Weedpacket

Yes: functions are defined at compile time, defined constants are evaluated at run time. ([man]define[/man] is just a function.)

[man]define[/man]

Defines a named constant at runtime.

[man]functions[/man]

Functions need not be defined before they are referenced, ...

Bonesnap

I understand that define is a function. I just found it odd that one could be used before being defined and another could not, but the compile-time vs. run-time makes sense. Thanks for replying!

Weedpacket

Bonesnap wrote:
I understand that define is a function. I just found it odd that one could be used before being defined and another could not,

Well, since [man]define[/man] is a function, it won't do anything until it's run - which by definition happens at run time.

NogDog

You might find this "interesting", too. 🙂

<?php

echo foo(); // works just fine

function foo()
{
	return "Hello";
}

if(true)
{
	echo bar(); // fatal error, function not defined

function bar()
{
	return "World";
}
}

Bonesnap

Weedpacket;11009483 wrote:
Well, since [man]define[/man] is a function, it won't do anything until it's run - which by definition happens at run time.

Makes sense!

NogDog;11009495 wrote:

You might find this "interesting", too. 🙂

<?php

echo foo(); // works just fine

function foo()
{
	return "Hello";
}

if(true)
{
	echo bar(); // fatal error, function not defined

function bar()
{
	return "World";
}
}

I do find that interesting. :eek: