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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0785.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0785.md | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0785.md b/compiler/rustc_error_codes/src/error_codes/E0785.md new file mode 100644 index 000000000..373320539 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0785.md @@ -0,0 +1,30 @@ +An inherent `impl` was written on a dyn auto trait. + +Erroneous code example: + +```compile_fail,E0785 +#![feature(auto_traits)] + +auto trait AutoTrait {} + +impl dyn AutoTrait {} +``` + +Dyn objects allow any number of auto traits, plus at most one non-auto trait. +The non-auto trait becomes the "principal trait". + +When checking if an impl on a dyn trait is coherent, the principal trait is +normally the only one considered. Since the erroneous code has no principal +trait, it cannot be implemented at all. + +Working example: + +``` +#![feature(auto_traits)] + +trait PrincipalTrait {} + +auto trait AutoTrait {} + +impl dyn PrincipalTrait + AutoTrait + Send {} +``` |