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Date: Wed, 15 Jul 2020 11:54:36 -0500
To: "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC][Discussion] Objects can be declared falsifiable
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Jul 15, 2020, at 11:43 AM, Marco Pivetta wrote:
> Hey Larry,
> 
> On Wed, Jul 15, 2020 at 5:32 PM Larry Garfield <larry@garfieldtech.com>
> wrote:
> 
> > 1) return null, which is a non-type, and thus you need to make the return
> > type ?User or User|null, which means the caller *must* always check it's
> > nullness.
> >
> > Allowing an object to falsify itself is a 4th,  more type-safe option.  It
> > lets you return an object that both fails a boolean check (like null) but
> > also has default values in it for the base case.  A user object likely
> > wouldn't use that, but a value object like an Address very well could.
> >
> > Until we can support for-reals monads (which would require enums and
> > generics to do properly; the former is possible the latter is very hard),
> > it's the best option we have for more type-safe returns.
> >
> 
> Adding a "falsey" state for code that expects `is_object($foo) === (bool)
> $foo` seems to be a massive BC break to me, and reduces type safety of
> boolean operators (and checks) by expanding the `object` type and all
> operators and expressions that can interact with it.
> 
> In general, `?T` is very much equivalent to `Maybe T`

I disagree entirely.  The value of a Maybe over just null is 

1) You can bind to it even if the result is empty; the "if is null" check gets abstracted away from the main code.
2) You are forced to unwrap/extract the value if you're not just binding, which makes it less likely you'll forget to check if it's null.

--Larry Garfield