sassnowski/option

A basic PHP implementation of the Option data type as found in Scala.

0.2.0 2016-05-04 21:29 UTC

Requires

• php: >=5.5

Requires (Dev)

• phpspec/phpspec: ~2.0

MIT

README

A PHP implementation of the Option data type from Scala (or Maybe from Haskell if you want).

DISCLAIMER: This package is not intented to be used in production. Its intend was to serve as a coding exercise to myself about how I would implement and Option Type in PHP. If you want to use this in production I'd recommend you use https://github.com/schmittjoh/php-option instead.

Installation

Install the package through composer:

$ composer require sassnowski/option

That’s it! Now you can use it in your code.

function divide($a, $b)
{
	if (0 === $b)
	{
		return Option::None();
	}
	
	return new Option($a / $b);
}

$result = divide(10, 5);
$result->get(); // 2

$result2 = divide(10, 0);
$result->isDefined(); // false

Summary

An Option represents an optional value, or in other words a value that may not exist. It is sometimes described as a List that contains a maximum of one item.

An Option is used in places where otherwise null might be used, e.g., the result of a Database Query. A more general way to put it is: A computation might return an Option if it is not defined for some inputs.

Option::map($func)

Using Options means that a lot of code needs to be aware of this data type. In order to still be able to reuse functions that operate on unwrapped values, this class provides a map function.

The purpose of the map function is to lift a function that normally operators on regular values to now work on Option values. Formally it turns a function of type

a -> b

into a function of type

Option a -> Option b

Example

// Note: This example uses PHP 7 type hinting. This is in no 
// way necessary for this package to work and is simply there 
// to illustrate the types that these functions are supposed to
// operate on.

function length(string $a): int
{
	return strlen($a);
}

$length1 = (new Option("abc"))->map('length');
$length1->isDefined(); // true
$length1->get(); // 3

// The length function never gets executed, since we're 
// dealing with an undefined value.
$length2 = Option::None->map('length');
$length2->isDefined(); // false
$length2->get(); // RuntimeException

The above example lifted the function length of type string -> int into a function of type Option string -> Option int. This means that we can still write and use functions that were written without optional values in mind and simply lift them to a function that can handle Options.

An important characteristic of the map method is, that the function that is being mapped over the option will never get executed if we’re dealing with an undefined value.

Option::flatMap($func)

Todo

Option::getOrElse($default)

Todo

Option::orElse($alternative)

Todo

Option::isDefined()

This function simply returns true if the value is anything other than null in which case it returns false.

License

MIT