1 A `where` clause contains a nested quantification over lifetimes.
3 Erroneous code example:
10 for<'a> &'a T: for<'b> Tr<'a, 'b>, // error: nested quantification
15 Rust syntax allows lifetime quantifications in two places within
16 `where` clauses: Quantifying over the trait bound only (as in
17 `Ty: for<'l> Trait<'l>`) and quantifying over the whole clause
18 (as in `for<'l> &'l Ty: Trait<'l>`). Using both in the same clause
19 leads to a nested lifetime quantification, which is not supported.
21 The following example compiles, because the clause with the nested
22 quantification has been rewritten to use only one `for<>`:
29 for<'a, 'b> &'a T: Tr<'a, 'b>, // ok