discriminated-union

Create an "algebraic data type" in pure PHP. There are many advantages to using ADT's, but most of them are moot in weak languages like PHP. Furthermore, there are many composer packages that implement this better than I have here - it is mostly an educational project.

NOTE: PHP 8.0 introduced the match keyword, meaning this Package will no longer work on PHP versions above 7.4

Make an Option Type

$Option = Union('Option')
            ->of('Success', fn($item)  => item)
            ->of('Error',   fn($error) => $error)
            ->render();

$failureExample = $Option->Error('Nothing worked right!');
$successExample = $Option->Success('Something went right!');

return match($successExample)->with(
  'Success' => fn($successObject) => $successObject,
  'Error'   => fn($errorObject)   => die()
)

So, what's going on here?

Algebraic data types are composite data types. They are sometimes called "Tagged Unions", "Discriminated Unions", or sometimes even just "enums". It's almost exactly the same as having three classes: an abstract superclass, and two children which cannot inherit one-another.

Think of a Pet class. A Pet can either be a dog or a cat.

$Pet = Union('Pet')->of('Dog')->of('Cat')->render();

You can own a "Dog", or you can own a "Cat". But under no circumstance can you own "just" a "Pet". It has to be one of those two.

Instantiate a new dog
$dog = $Pet->Dog

Now, imagine if we had fields such as "MeowCount" or "BarkCount". Only cats have meows and only dogs have barks. So you can use a Subtype Constructor to represent that:

$Pet = Union('Pet')
        ->of('Dog', fn($barkCount) => $barkCount)
        ->of('Cat', fn($meowCount) => $meowCount)

Now your functions can accept a Pet object.

function countNoises(/*$Pet*/ $pet) {

And you can exhaustively match all "arms" of your pet.

return match($pet)->with(
  'Dog'   => fn($barkCount) => "Dog barked $barkCount times",
  'Error' => fn($meowCount) => "Cat meowed $meowCount times"
);

License

This program can be licensed under the MIT license.