// core::fmt

impl DebugList<'_, '_> {
    fn entry_with<F>(&mut self, entry_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
}

impl DebugMap<'_, '_> {
    fn key_with<F>(&mut self, key_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
    
    fn value_with<F>(&mut self, value_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
}

impl DebugSet<'_, '_> {
    fn entry_with<F>(&mut self, entry_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
}

impl DebugStruct<'_, '_> {
    fn field_with<F>(&mut self, name: &str, field_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
}

impl DebugTuple<'_, '_> { // also DebugSet
    fn field_with<F>(&mut self, field_fmt: F) -> &mut Self
    where
        F: FnOnce(&mut Formatter) -> fmt::Result;
}