With dmd version 2.100.1,

rdmd --eval 'enum E : float{x, y} writeln(cast(float)E.x, " ", cast(float)E.y)'

prints "0, 1".

However, the spec states (17.2) that if a first member of enum type is not specified, it should be the .init value of the base type. Thus this example should print "nan nan".

Side note: the spec also states that if an unspecified member is equal to the member before it, the compiler should error. Technically that part is not violated by printing "nan nan" though because NaNs are not equal to themselves. The compiler does not currently error if the first member is explicitly set as nan so it behaves according to spec in that regard.