I recently posted a comment on a general tech group about this line of code:

define('WP_POST_REVISIONS', true);

Someone replied, "If the original coders don't know that you can't redefine a constant than why would you even trust any of their other code?"

That made me wonder, what mechanism in WordPress keeps themes/plugins/etc from redefining constants? I'm guessing that it has to do with the order in which code loads.

I recently posted a comment on a general tech group about this line of code:

define('WP_POST_REVISIONS', true);

Someone replied, "If the original coders don't know that you can't redefine a constant than why would you even trust any of their other code?"

That made me wonder, what mechanism in WordPress keeps themes/plugins/etc from redefining constants? I'm guessing that it has to do with the order in which code loads.

• constants

• 5 Constants are controlled at the PHP level, not the WP level. If a plugin tries to redefine a constant, it will throw a PHP error. There's no WordPress-specific magic here. – vancoder Commented May 8, 2020 at 16:50
• So, the mechanism is PHP. Does that mean that there is no place in the WordPress core that defines WP_POST_REVISIONS? I recently ran across 2 sites that neither showed the Revisions list, nor had the option in Screen Options. I had to add the code in wp-config – Nora McDougall-Collins Commented May 8, 2020 at 16:53
• 3 WP defines the constant only if it is not already defined: github/WordPress/WordPress/blob/master/wp-includes/… – vancoder Commented May 8, 2020 at 16:57
• 1 Exactly the information I needed! If you would make this answer, I will check it. – Nora McDougall-Collins Commented May 8, 2020 at 17:00

1 Answer 1

What mechanism does WordPress use to keep constants from being redefined?

None. Constants are not a WordPress feature, they're a part of the PHP programming language.

Someone replied, "If the original coders don't know that you can't redefine a constant than why would you even trust any of their other code?"

I think this is them suggesting that if the authors don't know that you cannot redefine a constant, then they might not be very good at PHP

That made me wonder, what mechanism in WordPress keeps themes/plugins/etc from redefining constants? I'm guessing that it has to do with the order in which code loads.

Once a constant is defined, it can't be changed. PHP enforces this, otherwise constants would just be fancy variables that can change on a whim.

Generally, it's considered poor practice to define those constants in plugins and themes. They're intended for wp-config.php and should be set by the user. I would treat any plugin or theme that defines WP constants with great suspicion and skepticism.