ajf/newtype

A handy function for creating opaque types

v1.0.3 2018-01-24 19:55 UTC

Requires

• php: >=7.0.0

Requires (Dev)

• phpunit/phpunit: ^5.0

LGPL-3.0-or-later

• Andrea Faulds

• PHP7

README

newType() is a handy function for creating opaque types, that is, a type that merely wraps another type. It takes two parameters: the name of your new wrapper type, and the name of the type you want to wrap. You get a class with a constructor taking a value of the wrapped type, and an ->unbox() method to get out the value of the wrapped type.

Require it with composer require ajf/newtype to use it. It's PHP 7-only, since PHP 7 is the first version of PHP with scalar type declarations. It would be possible to backport this, though.

An example of where you might use this:

<?php

namespace JaneBlogges\WonderfulApp;

use function ajf\newType\newType;

// Makes the new opaque type!
newType(FilePath::class, 'string');

function moveFile(FilePath $sourcePath, FilePath $destinationPath): bool {
    return rename($sourcePath->unbox(), $destinationPath->unbox());
}

moveFile(new FilePath('foo'), new FilePath('bar'));

Use it for that extra bit of type safety!

If you're after a mere alias that doesn't require explicit conversion to and from, check out PHP's built-in class\_alias function - though beware that only works with classes and not primitive types.

The name comes from Haskell's newtype declaration, which does the same thing:

newtype FilePath = FilePath String

It's similar to Hack's newtype declaration as well, although that works a little differently.