I'm in a situation where I try to define a function looking like this :

fn foo<N>(f: impl for<'a> Fn(&'a N, &'a [u32]) -> (impl Iterator<Item = N> + 'a)) { /* ... */ }

This code generate the following error :

error[E0562]: `impl Trait` is not allowed in the return type of `Fn` trait bounds

I want to express the fact the returned value of f depends on the lifetime 'a but I don't know who to write this with where close.
Something like this :

fn foo<N, FN, IN>(f: FN)
where
    FN: for<'a> Fn(&'a N, &'a [u32]) -> (IN + 'a),
    IN: Iterator<Item = N>,
{/* ... */}

Do you have any solution ?

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