error[E0119]: conflicting implementations of trait `From<()>` for type `S` --> $DIR/inter-crate-ambiguity-causes-notes.rs:9:1 | LL | impl From<()> for S { | ------------------- first implementation here ... LL | impl From for S | ^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S` | = note: upstream crates may add a new impl of trait `std::iter::Iterator` for type `()` in future versions error: aborting due to previous error For more information about this error, try `rustc --explain E0119`.