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Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0316.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0316.md | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0316.md b/compiler/rustc_error_codes/src/error_codes/E0316.md new file mode 100644 index 000000000..4368c3217 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0316.md @@ -0,0 +1,32 @@ +A `where` clause contains a nested quantification over lifetimes. + +Erroneous code example: + +```compile_fail,E0316 +trait Tr<'a, 'b> {} + +fn foo<T>(t: T) +where + for<'a> &'a T: for<'b> Tr<'a, 'b>, // error: nested quantification +{ +} +``` + +Rust syntax allows lifetime quantifications in two places within +`where` clauses: Quantifying over the trait bound only (as in +`Ty: for<'l> Trait<'l>`) and quantifying over the whole clause +(as in `for<'l> &'l Ty: Trait<'l>`). Using both in the same clause +leads to a nested lifetime quantification, which is not supported. + +The following example compiles, because the clause with the nested +quantification has been rewritten to use only one `for<>`: + +``` +trait Tr<'a, 'b> {} + +fn foo<T>(t: T) +where + for<'a, 'b> &'a T: Tr<'a, 'b>, // ok +{ +} +``` |