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Date: Thu, 27 May 2021 14:23:10 +0100
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Subject: Re: [PHP-DEV] Consensus Gathering: is_initialized
From: rowan.collins@gmail.com (Rowan Tommins)

On 27/05/2021 13:07, Pierre wrote:
> So, if it's going to be used and abused in those magic APIs we all use 
> daily without thinking about it (let's say, hydrators or serializers, 
> dependency injection containers and all that stuff, and you do 
> maintain some if I recall) and unlock some performance optimizations 
> in there, I'd say go for it. 


I think "abused" is the right word here. The uninitialized state exists 
in the first place because we don't have a way to enforce initialization 
in constructors, not because we really wanted a new special value that 
is "like null, but even more so".

The combination of union types and enums actually gives a much more 
expressive way of representing "valid value or explicit null or special 
default". To use the ORM lazy-loading example:


enum ORMState {
     case Unloaded;
}

class Example {
     private int|ORMState|null $foo = ORMState::Unloaded;

     public function getFoo(): ?int {
         if ( $this->foo === ORMState::Unloaded ) {
             $this->foo = $this->loadFromDatabase('foo');
         }
         return $this->foo;
     }

     private function loadFromDatabase($fieldName): ?int {
         echo "Fetching '$fieldName' from database...\n";
         return 42;
     }
}

// Create object; note there's no constructor, but the property has a 
default so is never uninitialized
$obj = new Example;
// On first call to method, the default value is detected and the 
property lazy-loaded
var_dump($obj->getFoo());
// Subsequent accesses return the loaded value directly, at the cost of 
a single strict comparison, no magic function needed
var_dump($obj->getFoo());


Unlike abusing "uninitialized" as a third state (next to int and null), 
this allows any number of states to be recorded, and treated 
appropriately. For instance, an auto-increment key might default to 
ORMState::NotYetCalculated, and trigger an error rather than a lazy-load.


Regards,

-- 
Rowan Tommins
[IMSoP]