diff options
| -rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0604.md | 11 | ||||
| -rw-r--r-- | compiler/rustc_typeck/src/check/cast.rs | 1 |
2 files changed, 9 insertions, 3 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0604.md b/compiler/rustc_error_codes/src/error_codes/E0604.md index adbf76509ed..806f0001c60 100644 --- a/compiler/rustc_error_codes/src/error_codes/E0604.md +++ b/compiler/rustc_error_codes/src/error_codes/E0604.md @@ -6,11 +6,16 @@ Erroneous code example: 0u32 as char; // error: only `u8` can be cast as `char`, not `u32` ``` -As the error message indicates, only `u8` can be cast into `char`. Example: +`char` is a Unicode Scalar Value, an integer value from 0 to 0xD7FF and +0xE000 to 0x10FFFF. (The gap is for surrogate pairs.) Only `u8` always fits in +those ranges so only `u8` may be cast to `char`. + +To allow larger values, use `char::from_u32`, which checks the value is valid. ``` -let c = 86u8 as char; // ok! -assert_eq!(c, 'V'); +assert_eq!(86u8 as char, 'V'); // ok! +assert_eq!(char::from_u32(0x3B1), Some('α')); // ok! +assert_eq!(char::from_u32(0xD800), None); // not a USV. ``` For more information about casts, take a look at the Type cast section in diff --git a/compiler/rustc_typeck/src/check/cast.rs b/compiler/rustc_typeck/src/check/cast.rs index a397ee771af..f6b5e0084d1 100644 --- a/compiler/rustc_typeck/src/check/cast.rs +++ b/compiler/rustc_typeck/src/check/cast.rs @@ -337,6 +337,7 @@ impl<'a, 'tcx> CastCheck<'tcx> { self.expr_ty ) .span_label(self.span, "invalid cast") + .span_help(self.span, "try `char::from_u32` instead") .emit(); } CastError::NonScalar => { |