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pub trait Variadic<T, A = T, B = A, C = B> { type OneLess: Variadic<A, B, C>; fn pop(self) -> (Option<T>, Self::OneLess); } pub struct VarArgs4<A, B, C, D>(A, B, C, D); pub struct VarArgs3<A, B, C>(A, B, C); pub struct VarArgs2<A, B>(A, B); pub struct VarArgs1<A>(A); pub struct VarArgs0<A> { _m: std::marker::PhantomData<A>, } impl<T, A, B, C> Variadic<T, A, B, C> for VarArgs4<T, A, B, C> { type OneLess = VarArgs3<A, B, C>; fn pop(self) -> (Option<T>, Self::OneLess) { let VarArgs4(t, a, b, c) = self; (Some(t), VarArgs3(a, b, c)) } } impl<T, A, B> Variadic<T, A, B> for VarArgs3<T, A, B> { type OneLess = VarArgs2<A, B>; fn pop(self) -> (Option<T>, Self::OneLess) { let VarArgs3(t, a, b) = self; (Some(t), VarArgs2(a, b)) } } impl<T, A> Variadic<T, A> for VarArgs2<T, A> { type OneLess = VarArgs1<A>; fn pop(self) -> (Option<T>, Self::OneLess) { let VarArgs2(t, a) = self; (Some(t), VarArgs1(a)) } } impl<T> Variadic<T> for VarArgs1<T> { type OneLess = VarArgs0<T>; fn pop(self) -> (Option<T>, Self::OneLess) { let VarArgs1(t) = self; (Some(t), VarArgs0 { _m: std::marker::PhantomData }) } } impl<T> Variadic<T> for VarArgs0<T> { type OneLess = VarArgs0<T>; fn pop(self) -> (Option<T>, Self) { (None, VarArgs0 { _m: std::marker::PhantomData }) } }