Re: PHP 7.1 - Address PHPSadness #28?

Robert Williams wrote on 14/09/2015 23:46:

Nonsense. It just means that one isn’t using null the way you do. You’re saying people shouldn’t be programming to distinguish between declared-but-defined-null and undeclared. But the fact is, from user land-POV, null*is* a value, and it’s frequently used where a variable needs to be defined with a sentinel value that clearly flags the variable as not having an otherwise valid value. The alternative is to use magic values as sentinels instead — e.g., 0 or 9999 for an integer, or empty-string for a string — but that causes all sorts of bugs when those values are only rarely legitimate versus never legitimate (see: Y2K). Magic values also tend to make code less readable.

Absolutely. However, in order to need a dynamic check of variable existence, you must also be using non-existence as a second sentinel value. You must be saying "if the variable has never been assigned to, that means state X; if it's been assigned a null value, that means state Y". My argument is that using undefined variables like that is a bad choice of sentinel value, and if you need more than one sentinel value in the first place, you probably need a more complex data type (a struct-like object with separate state and value properties, for instance).

Incidentally, what’s the difference, philosophically, between these two: $foo = null; var_dump(isset($foo)); //false $foo = [‘bar’ => null]; var_dump(array_key_exists(‘bar’, $foo)); //true

The difference is that when you define $foo, you have chosen that label directly as part of your source code - just like you'd name a class or function. You *know* that the variable exists, so the only interesting question is whether it has a "real" value or a "default" value. In an explicit declaration like that, you have also chosen 'bar' directly, but the difference becomes clearer with a more dynamic example: $foo = []; $foo[ $key ] = null; var_dump(array_key_exists(‘bar’, $foo)); // interesting value Here, the value $key is something which can only be known at run-time; consequently, you cannot know without running the code whether the array key will in fact exist. That makes checking for its existence at runtime a useful ability. The fact that the internal implementation of the symbol table is similar to that of an associative array doesn't justify making them identical to the user. Regards, -- Rowan Collins [IMSoP]