Select enum constants from boolean[] or bit mask

[runeflobakk]

Use a bit mask to select constants from an enum, based on which indices which are set (1-bits):

<E extends Enum<E>> Stream<E> DiggEnums.selectByBitmask(BitSet, Class<E>)

Use an array of booleans to select constants from an enum, based on which indices which are true;

<E extends Enum<E>> Stream<E> DiggEnums.selectByIndexAsOrdinals(boolean[], Class<E>)

Use case

This is obviously a bit esoteric functionality. The intention is to ease the use of some APIs which may (probably for valid performance reasons, at least at the time the APIs were defined) return a kind of bitmask to represent a standardized set of possibly set or unset values.

An example of this is X509Certificate.getKeyUsage(), which returns an array of booleans, where each element's position in the array indicate if a known set of ordered values is true or false. This will enable e.g. the following:

/// Enum representation of the X.509 KeyUsage extension (OID = 2.5.29.15).
/// The order of constants reflect the order of the ASN.1 definition, see
/// [X509Certificate#getKeyUsage()].
enum KeyUsage {
    digitalSignature,
    nonRepudiation,
    keyEncipherment,
    dataEncipherment,
    keyAgreement,
    keyCertSign,
    cRLSign,
    encipherOnly,
    decipherOnly;

    static Stream<KeyUsage> allFrom(X509Certificate certificate) {
        return selectByIndexAsOrdinals(certificate.getKeyUsage(), KeyUsage.class);
    }
}

Note on EnumSet

Java already has a way to represent a set of enum constants using a compact and efficient bitmask, but no way to construct the EnumSet using a bitmask as the source.