enum Linear
{
    one = 1,
    two = 2
}

static assert(is(typeof(unsafeEnumFromIndex!Linear(0)) == Linear));
assert(unsafeEnumFromIndex!Linear(0) == Linear.one);
assert(unsafeEnumFromIndex!Linear(1) == Linear.two);

enum Mixed
{
    one = 1,
    oneAgain = 1,
    two = 2
}

assert(unsafeEnumFromIndex!Mixed(0) == Mixed.one);
assert(unsafeEnumFromIndex!Mixed(1) == Mixed.one);
assert(unsafeEnumFromIndex!Mixed(2) == Mixed.two);