多分 let a: impl Future<Item = A>; let b: impl Future<Item = Result<T, E>>; みたいな2つのFutureで a.join(b).then(|(a, b)| ... ); とする話だと思うが合ってます…?
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多分 let a: impl Future<Item = A>; let b: impl Future<Item = Result<T, E>>; みたいな2つのFutureで a.join(b).then(|(a, b)| ... ); とする話だと思うが合ってます…?