Variable key on php enum

It's important to distinguish between three different things here:

• A class property would be declared in a class as static $foo (with optional visibility, type, and default value), and accessed as Example::$foo. Dynamically, you could access that with "variable-variable" syntax, e.g. $name = 'foo'; echo Example::$$name;.
• A class constant would be declared as const foo = 'value' (with optional visibility), and accessed as Example::foo. From PHP 8.3 onwards, you could access that dynamically with $name = 'foo'; echo Example::{$name};. In earlier versions, there was no direct syntax, but you could use the constant function, as in $name = 'foo'; echo constant("Example::$name");
• An enum case is declared as case foo (with a value if using a "backed enum"), and it is accessed using the same syntax as a class constant.

In fact, an enum case is treated like a constant in many ways, and a test shows that both the constant function and the PHP 8.3 dynamic constant syntax can be used to look one up, so this will work:

enum ExampleEnum
{
    case _1;
    case _2;

    public function getIt(): string
    {
        return match ($this) {
            ExampleEnum::_1 => 'foo',
            ExampleEnum::_2 => 'bar',
        };
    }
}

$id = "_1";

// PHP 8.3 or later only:
echo ExampleEnum::{$id}->getIt();

// any version supporting enums (PHP 8.0 or later):
echo constant("ExampleEnum::$id")->getIt();

Note that if you use a "backed enumeration", you can associate an arbitrary integer or string with each case, separate from its name, and use the from method to look up a case based on that value.