How to check if non-backed enum contains case?

I have basic enum

enum Fruit
{
  case APPLE;
  case ORANGE;
  case BANANA;
}

and some function that uses typing with that enum:

function eatFruit (Fruit $fruit)
{
  // do stuff
}

and variable with unknown content

$fruit = $_POST['fruit']; // user choosed "MILK"
if (?????) { // how to check if it's fruit?
  eatFruit($fruit); // this should not be executed
}

I cannot find in documentation simple way to check if enum contains specific case.

It is possible with backed enums like that

enum Fruit
{
  case APPLE = 'APPLE';
  case ORANGE = 'ORANGE';
  case BANANA = 'BANANA';
}

Fruit::from('');
Fruit::tryFrom('');

This will work, but from does not exist on non-backed enums form my first example.

Fatal error: Uncaught Error: Call to undefined method Fruit::from()

You can use the static method cases() for this. This returns an array of all values in the enum. The values have a "name" property that is a string representation you can check against (backed enums also have a "value" property that contains the string value you defined in the enum).

So an example implementation could be something like:

enum Fruit {
    case APPLE;
    case ORANGE;
    case BANANA;
}

// String from user input
$fruit = $_POST['fruit'];

// Find matching fruit in all enum cases
$fruits = Fruit::cases();
$matchingFruitIndex = array_search($fruit, array_column($fruits, "name"));

// If found, eat it
if ($matchingFruitIndex !== false) {
    $matchingFruit = $fruits[$matchingFruitIndex];
    eatFruit($matchingFruit);
} else {
    echo $fruit . " is not a valid Fruit";
}

function eatFruit(Fruit $fruit): void {
    if ($fruit === Fruit::APPLE) {
        echo "An apple a day keeps the doctor away";
    } elseif ($fruit === Fruit::ORANGE) {
        echo "When life gives you oranges, make orange juice";
    } elseif ($fruit === Fruit::BANANA) {
        echo "Banana for scale";
    }
}

Working version with sample data: https://3v4l.org/ObD3s

If you want to do this more often with different enums, you could write a helper function for this:

function getEnumValue($value, $enumClass) {
    $cases = $enumClass::cases();
    $index = array_search($value, array_column($cases, "name"));
    if ($index !== false) {
        return $cases[$index];
    }
    
    return null;
}

$fruit = getEnumValue($_POST['fruit'], Fruit::class);
if ($fruit !== null) {
    eatFruit($fruit);
} else {
    echo $_POST['fruit'] . " is not a valid Fruit";
}

Example with the same sample data: https://3v4l.org/bL8Wa