From a15cb49362971a360c5fd0ad88e7add3bd9ac5d6 Mon Sep 17 00:00:00 2001 From: George Bateman Date: Tue, 14 Dec 2021 21:49:49 +0000 Subject: #91836: Clarify error on casting larger integers to char --- compiler/rustc_error_codes/src/error_codes/E0604.md | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'compiler/rustc_error_codes/src') 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 -- cgit 1.4.1-3-g733a5