Is it possible to define the type of a parameter as enum values? – Php

The Problem:

In a function, is it possible to specify that a parameter can only take certain predefined values (e.g., from an enum)? How can this be achieved in a language like PHP or Java?

The Solutions:

Solution 1: Use an Enum as typehint or `tryFrom()`

If you know the parameter will always be an instance of an Enum, you can use the Enum as the typehint:

public function getValuesFromType(MyTypeEnum $type)

However, if you don’t know the type of the parameter, you can use tryFrom() static function on the Enum:

public function getValuesFromType(string $type) {
    $myType = MyTypeEnum::tryFrom($type);

    if (!$myType) {
       // handle null state
    }

    // $myType is a valid MyTypeEnum instance
}

tryFrom() will return null if the value is not matching with any case.

Solution 2: Add a function to the Enum for values

You can add a function to the Enum to return the values associated with it:

enum MyTypeEnum
{
    case APPLE = 'apple';
    case BANANA = 'banana';

    public function values() {
        return match($this) {
            self::APPLE => ['red', 'green'],
            self::BANANA => ['yellow', 'brown']
        }
    }
}

Usage:

MyTypeEnum::tryFrom('apple')?->values() // return ['red', 'green']
MyTypeEnum::tryFrom('orange')?->values() // return null
MyTypeEnum::tryFrom('orange')?->values() ?? [] // return []

Solution 2: Using a non-backed enum in conjunction with PHP 8.3 and Symfony 6.3

In PHP 8.3, you can define a non-backed enum by specifying the type of the enum as a string. This allows you to restrict the values that can be passed as parameters to a function.

For example, the following function takes a non-backed enum as a parameter:

public function getValuesFromType(MyTypeEnum $type)

The MyTypeEnum enum can be defined as follows:

<?php

namespace App\Enum;

enum MyTypeEnum:string {
    case CHOICE_ONE = 'ONE';
    case CHOICE_TWO = 'TWO';
}

When you call the getValuesFromType() function, you can pass only the values defined in the enum as the parameter. For example, the following code will work:

$type = MyTypeEnum::CHOICE_ONE;
$values = $this->getValuesFromType($type);

However, the following code will throw an error:

$type = 'THREE';
$values = $this->getValuesFromType($type);

This is because the value ‘THREE’ is not defined in the MyTypeEnum enum.

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