Use AnyErrorOf in Future::ThenIfSuccess #4803
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`Future::ThenIfSuccess` allows to chain a continuation to a future that is only executed when the future completes with no error. In terms of types that means we have a `Future<Result<T, E>>`, call `.ThenIfSuccess` with a closure `T -> U` or `T -> Result<U, E>` and the result will be a `Future<Result<U, E>>` in both cases. Imagine you want to chain a closure `T -> Result<U, E2>`. This is currently not supported due to the mismatching error types. This changes with this PR. `Future<Result<T, E>>::ThenIfSuccess<T -> Result<U, E2>>()` will result in a `Future<Result<U, AnyErrorOf<E, E2>>>`. That allows easier composition of closures with different error types. Note that this changes the semantics of `ThenIfScuccess` and I had to make some changes in existing code to avoid behavioural changes.
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Future::ThenIfSuccessallows to chain a continuation to a future that is only executed when the future completes with no error.In terms of types that means we have a
Future<Result<T, E>>, call.ThenIfSuccesswith a closureT -> UorT -> Result<U, E>and the result will be aFuture<Result<U, E>>in both cases (that's the status quo).Imagine you want to chain a closure
T -> Result<U, E2>. This is currently not supported due to the mismatching error types.This changes with this PR.
Future<Result<T, E>>::ThenIfSuccess<T -> Result<U, E2>>()will result in aFuture<Result<U, AnyErrorOf<E, E2>>>. That allows easier composition of closures with different error types.Note that this changes the semantics of
ThenIfScuccessand I had to make some changes in existing code to avoid behavioural changes.