Function safina_select::select_abc

pub async fn select_abc<A, B, C, FutA, FutB, FutC>(
    a: FutA, 
    b: FutB, 
    c: FutC
) -> OptionAbc<A, B, C> where
    FutA: Future<Output = A> + Send + 'static,
    FutB: Future<Output = B> + Send + 'static,
    FutC: Future<Output = C> + Send + 'static, 

Awaits the futures and returns the value from the one that completes first.

First moves them to the heap, to make them Unpin. Use SelectFuture::new to avoid allocating on the heap.