It's quite popular I would say: https://github.com/search?q=BoxTryFuture&type=code

It's quite popular I would say: https://github.com/search?q=BoxTryFuture&type=code

Only 4 seem to be unique (tide, tinychain, txn_lock, tokio-tide, and tokio-tide's code is in comment). All the others seem to be forks of tide and tinychain.

You're right. So you consider this extra for now? I still think that this is quite useful.

Also, the search can be extended by looking for the usage of BoxFuture<Result*.

I can see that the usage of BoxTryFuture<Ok, Err> instead of BoxFuture<Result<Ok, Err>> could be controversial. Especially in cases when Error is hidden in a type alias like BoxFuture<Result<Ok>>, because for someone the last one is more convenient. But refactoring this:

async fn get<'a>(&'a self) -> BoxStream<'a,  Result<BoxFuture<'a, Result<T, Error>>, Error>> {

to this:

type ItemStream<'a, T, Err> = BoxTryStream<'a,  BoxTryFuture<'a, T, Err>, Err>>;

async fn get<'a>(&'a self) -> ItemStream<'a, T, Error> {

made my day :)