option_iter.rs

// Turns out that this iterator is unnecessary since the std::option::Option type
// itself implements this exact semantics


/// An iterator that yields an element once or never.
///
/// This `struct` is created by the [`once_if_ever`] function. See its documentation for more.
pub struct OnceIfEver<T> {
    value: Option<T>,
}

impl<T> Iterator for OnceIfEver<T> {
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> {
        mem::replace(&mut self.value, None)
    }
}

/// Creates an iterator that yields an element once or never.
fn once_if_ever<T>(v: Option<T>) -> OnceIfEver<T> {
    OnceIfEver { value: v }
}