[BrandonM]

I would argue that it makes a lot more sense for a non-number to return NULL than to return 0. If it returns 0, how do you distinguish between "0" and ""? At least with a NULL return value you can use the function to see if you're even looking at a number at all.

[city41]

Sure. And I haven't used PHP in about a decade. But it sounds to me like this was overlooked by them and so returned 0 for many years. Despite being undocumented behavior, fixing it causes a breaking change. On my team whenever we come into this situation and realize that fixing overlooked things can actually "break" people, we really think twice about the fix. Even if in theory the fix on its own is totally the right thing to do.

[Nwallins]

> fixing it causes a breaking change. On my team whenever we come into this situation and realize that fixing overlooked things can actually "break" people, we really think twice about the fix.

Answered in the 2nd comment from Rasmus:

If this was changed in a minor version, I'd agree with you on the BC change, but we have been working on catching these weird edge-case scenarios that lead to unexpected bugs.

i.e. they thought about it and decided this version was an acceptable one for making breaking changes.