pub trait RestrictiveFn: Fn(&mut i32) + Send + Sync + 'static { }
impl<T> RestrictiveFn for T where T: Fn(&mut i32) + Send + Sync + 'static { }

struct Fine {
    member: Box<Fn(&mut i32) + Send + Sync + 'static>,
}

struct Confusing {
    member: Box<RestrictiveFn>,
}

struct VerboseButOk {
    member: Box<RestrictiveFn<Output=()>>,
}

pub trait ReturnDoesNotHelp: Fn(&mut i32) -> () + Send + Sync + 'static { }
impl<T> ReturnDoesNotHelp for T where T: Fn(&mut i32) -> () + Send + Sync + 'static { }

struct ConfusingAgain {
    member: Box<ReturnDoesNotHelp>,
}


fn main() { }