[array_key_first]

I mean from a static analysis perspective - type annotations in PHP actually do stuff, and you can type annotate pretty much everything. And people actually do it.

Also, you can just flip on strict typing in PHP, and you should know that.

[tuqqu]

Strict types determine whether a function accepts a variable of a certain type, casts it, or throws a TypeError. It does not affect int + string operations or anything else really

[array_key_first]

Kind of but not really. Even without strict types, functions will throw a type error if you give them the wrong thing for almost all types, except primitives, which will be automatically coerced. Strict types turns that coercion off.

Really, that's probably enough for a lot of cases, because PHP doesn't have operator overloading. Yes, you can add '10' + 10 and get 20, but not if either of those go into any function. If you have a function that needs to do string stuff, you take string stuff in, and you don't have to worry about string operations or coercing ints or anything.