Option Type for PHP
, (*1)
A PHP implementation of the Option data type from Scala (or Maybe from Haskell if you want)., (*2)
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., (*3)
Installation
Install the package through composer:, (*4)
$ composer require sassnowski/option
That’s it! Now you can use it in your code., (*5)
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);
$result->isDefined(); // false
Summary
An Option represents an optional value, or in other words a value that may not exist. It is sometimes described as a List that contains a maximum of one item., (*6)
An Option is used in places where otherwise null might be used, e.g., the result of a Database Query. A more general way to put it is: A computation might return an Option if it is not defined for some inputs., (*7)
Option::map($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., (*8)
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, (*9)
a -> b
into a function of type, (*10)
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
$length2->get(); // RuntimeException
The above example lifted the function length of type string -> int into a function of type Option string -> Option int. This means that we can still write and use functions that were written without optional values in mind and simply lift them to a function that can handle Options., (*11)
An important characteristic of the map method is, that the function that is being mapped over the option will never get executed if we’re dealing with an undefined value., (*12)
Option::flatMap($func)
Todo, (*13)
Option::getOrElse($default)
Todo, (*14)
Option::orElse($alternative)
Todo, (*15)
Option::isDefined()
This function simply returns true if the value is anything other than null in which case it returns false., (*16)
License
MIT, (*17)
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