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Message-ID: <12345f19-d387-4984-63db-2ee677e34a7a@gmail.com>
Date: Thu, 12 May 2016 15:26:27 +0100
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Subject: Re: [PHP-DEV] Re: [RFC][VOTE] Nullable Types
From: rowan.collins@gmail.com (Rowan Collins)

On 12/05/2016 14:46, Lester Caine wrote:
> The key element *I* of cause am miss reading is the (Bar ...) which is a
> type hint. That will not exist in any of the code prior to ? and that is
> the key to what is being discussed. No type hint ... no change?
>
> If someone 'improves' a third party library by adding type hints then
> this is were the using code needs to be checked?

Correct. It should be no different from what can be done with existing 
type hints - if I change a library you were using from "function 
foo($bar)" to "function foo(Bar $bar)", it's possible you were passing a 
different object in and will now get an error.

If my library was always expecting Bar objects anyway, I'm arguably 
doing you a favour by forcing you to fix a long-standing bug where you 
passed the wrong thing.


The way I like to think about type hints in PHP is sugar for assertions 
at the top of the function:

function foo(Bar $bar) {
#...
}

is roughly equivalent to:

funtion foo($bar) {
assert($bar instanceOf Bar);
#...
}


The new syntax is just a different sugar, so that:

function foo(?Bar $bar) {
#...
}

is roughly equivalent to:

funtion foo($bar) {
assert(is_null($bar) || $bar instanceOf Bar);
#...
}


If the language didn't support typehints at all, I could add assertions 
like that in my library, and cause basically the same behaviour if you 
call my functions the wrong way.

[Strictly, in PHP 7, it's more like "if ( ! CHECK ) { throw new 
TypeError; }" rather than assert(), but the default result is the same.]

Regards,
-- 
Rowan Collins
[IMSoP]