diff options
| -rw-r--r-- | compiler/rustc_hir_typeck/src/upvar.rs | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/compiler/rustc_hir_typeck/src/upvar.rs b/compiler/rustc_hir_typeck/src/upvar.rs index 3c5fcdd005e..43e3ebde67c 100644 --- a/compiler/rustc_hir_typeck/src/upvar.rs +++ b/compiler/rustc_hir_typeck/src/upvar.rs @@ -1690,6 +1690,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { // // If the data will be moved out of this place, then the place will be truncated // at the first Deref in `adjust_for_move_closure` and then moved into the closure. + // + // For example: + // + // struct Buffer<'a> { + // x: &'a String, + // y: Vec<u8>, + // } + // + // fn get<'a>(b: Buffer<'a>) -> impl Sized + 'a { + // let c = move || b.x; + // drop(b); + // c + // } + // + // Even though the closure is declared as move, when we are capturing borrowed data (in + // this case, *b.x) we prefer to capture by reference. + // Otherwise you'd get an error in 2021 immediately because you'd be trying to take + // ownership of the (borrowed) String or else you'd take ownership of b, as in 2018 and + // before, which is also an error. hir::CaptureBy::Value { .. } | hir::CaptureBy::Use { .. } if !place.deref_tys().any(Ty::is_ref) => { |