Function gluon_base::merge::merge3

pub fn merge3<F, A, B, C, R>(
    a_original: &A,
    a: Option<A::Owned>,
    b_original: &B,
    b: Option<B::Owned>,
    c_original: &C,
    c: Option<C::Owned>,
    f: F
) -> Option<R>
where
    A: ToOwned + ?Sized,
    B: ToOwned + ?Sized,
    C: ToOwned + ?Sized,
    F: FnOnce(A::Owned, B::Owned, C::Owned) -> R,