Missing scala.Tuple.flatMap

[nicolasstucki]

Compiler version

3.0

Description

We have Tuple.FlatMap to compute the type of Tuple.flatMap but we do not implement Tuple.flatMap.

We should implement it in a similar way as what is described in #12888.

[nicolasstucki]

Tests can be added to tests/pos/tuple-flatmap.scala.

[FunFunFine]

What's about other methods, e.g. fold? Its implementation is missing too

[nicolasstucki]

Not sure how a fold signature would look like. It is worth exploring. I'm not so sure that this method would be useful, it might end up equivalent to tup.toList.foldLeft(...).

[nicolasstucki]

We have a good implementation in #13245, but the signature is not ideal. We should revisit this PR in the future when we have more flexibility with type arguments (such as defining def f[T][U]).

[SethTisue]

we have def f[T][U] now (SIP-47), does it help?