// First: Define your flags type. It needs to be a newtype over its underlying bits type
pub struct ManualFlags(u32);

// Next: use `impl Flags` instead of `struct Flags`
bitflags! {
    impl ManualFlags: u32 {
        const A = 0b00000001;
        const B = 0b00000010;
        const C = 0b00000100;
        const ABC = Self::A.bits() | Self::B.bits() | Self::C.bits();
    }
}

// First: Define your flags type. It just needs to be `Sized + 'static`.
pub struct ManualFlags(u32);

// Not required: Define some constants for valid flags
impl ManualFlags {
    pub const A: ManualFlags = ManualFlags(0b00000001);
    pub const B: ManualFlags = ManualFlags(0b00000010);
    pub const C: ManualFlags = ManualFlags(0b00000100);
    pub const ABC: ManualFlags = ManualFlags(0b00000111);
}

// Next: Implement the `BitFlags` trait, specifying your set of valid flags
// and iterators
impl Flags for ManualFlags {
    const FLAGS: &'static [Flag<Self>] = &[
        Flag::new("A", Self::A),
        Flag::new("B", Self::B),
        Flag::new("C", Self::C),
    ];

    type Bits = u32;

    fn bits(&self) -> u32 {
        self.0
    }

    fn from_bits_retain(bits: u32) -> Self {
        Self(bits)
    }
}