Sometimes, we need to impl trait for tuple. The solution is macro_rules, for example:

macro_rules! impl_query {
    ($($i: literal),+ $(,)?) => {
        paste! {
            impl<$([<T $i>]),+, C> Query<C, ((),)> for ($([<T $i>]),+,)
            where
                $([<T $i>]: IntoIterator<Item = C>),+,
                C: Borrow<Course>,
            {
                fn into_iter(self) -> impl Iterator<Item = C> {
                    IntoIterator::into_iter([])$(.chain(self.$i))*
                }
            }
        }
    };
}

Then we need:

impl_query!(0,);
impl_query!(0, 1,);
impl_query!(0, 1, 2);
impl_query!(0, 1, 2, 3);
impl_query!(0, 1, 2, 3, 4);
impl_query!(0, 1, 2, 3, 4, 5);

This is hard to write. So I tried:

macro_rules! gen_impl {
    ($macro: ident, $first: literal) => {
        $macro!($first);
    };
    ($macro: ident, $first: literal, $($i: literal),*$(,)?) => {
        $macro!($first, $($i),*);
        gen_impl!($macro, $($i),*);
    };
}

gen_impl!(impl_query, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0);

Is there better method to do this? Or have there been any crate to help with this?

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