PHPのお勉強！ – Atelier ”慶”

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列挙型と static メソッド

列挙型は、static メソッドを持つこともできます。列挙型で static メソッドを使う主な理由は、コンストラクタの代わりをさせるためです。たとえば、以下のようなものです:

<?php

enum Size
{
    case Small;
    case Medium;
    case Large;

    public static function fromLength(int $cm): static
    {
        return match(true) {
            $cm < 50 => static::Small,
            $cm < 100 => static::Medium,
            default => static::Large,
        };
    }
}
?>

static メソッドには public, private, protected が指定できますが、列挙型では実際 private と protected は同じものです。なぜなら、継承が許されていないからです。

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User Contributed Notes 5 notes

down

niloofarfs ¶

2 years ago

To get all scalar equivalents values of Backed Enum as an array you could define a method in your Enum:

<?php

enum Suit: string
{
    case Hearts = 'H';
    case Diamonds = 'D';
    case Clubs = 'C';
    case Spades = 'S';

    public static function values(): array
    {
       return array_column(self::cases(), 'value');
    }
}

?>

down

joe502357217 at qq dot com ¶

1 year ago

You simply need to use the following code as a replacement for the example provided by Aaron Saray.
This piece of code is more concise.

<?php
enum Suit: string
{
    case Hearts = 'H';
    case Diamonds = 'D';
    case Clubs = 'C';
    case Spades = 'S';

    public static function forSelect(): array
    {
        return array_column(self::cases(), 'name', 'value');
    }
}

var_dump(Suit::forSelect());
?>

down

Ulf ¶

1 year ago

Note, that enums are internally declared as final and thus, cannot extend each other (though, they are allowed to extend other classes).

That also means, that the "Size::fromLength()" method from this page's example redundantly uses "static::" (because there's no late static binding required), and could easily use "self::" or "Size::" instead.

See: https://php.watch/versions/8.1/enums#enum-inheritance

down

Aaron Saray ¶

2 years ago

Need to retrieve all the names and values immediately from a backed enum (for something like a select box) and you don't want to loop over `Enum::cases()`?  Try this:

<?php
enum Suit: string
{
    case Hearts = 'H';
    case Diamonds = 'D';
    case Clubs = 'C';
    case Spades = 'S';

    public static function forSelect(): array 
    {
      return array_combine(
        array_column(self::cases(), 'value'),
        array_column(self::cases(), 'name')
      );
    }
}

Suit::forSelect();
?>

Put `forSelect()` in a trait and use it in any enum you have that needs this functionality.

down

lokashafeek7755 at gmail dot com ¶

1 year ago

If you want to supplement the key-value pairs with additional descriptions for each enum value in the forSelect method, you can modify the array structure to include an associative array for each enum value. Here's an example:

<?php 

enum Gender:int
{
    case Male = 1;
    case Female = 2;

    public static function forSelect(): array
    {
        return [
            self::Male->value => [
                'label' => 'Male',
                'description' => 'This is the Male gender',
            ],
            self::Female->value => [
                'label' => 'Female',
                'description' => 'This is the Female gender',
            ],
        ];
    }

}
?>

In this updated example, each enum value is represented as an associative array with two keys: 'label' and 'description'. You can customize the label and description for each enum value accordingly.

Please note that to access the label and description for a specific enum value, you would need to use the corresponding array keys. For example, to get the label for the Male gender, you can use self::forSelect()[self::Male->value]['label'].

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