Nim is stack allocated unless you specifically mark a type as a reference, and "does not use classical GC algorithms anymore but is based on destructors and move semantics": https://nim-lang.org/docs/destructors.html
Where Rust won't compile when a lifetime can't be determined, IIRC Nim's static analysis will make a copy (and tell you), so it's more as a performance optimisation than for correctness.
Regardless of the details and extent of the borrow checking, however, it shows that it's possible in principle to infer lifetimes without explicit annotation. So, perhaps C++ could support it.
As you say, it's the semantics of the syntax that matter. I'm not familiar with C++'s compiler internals though so it could be impractical.
Where Rust won't compile when a lifetime can't be determined, IIRC Nim's static analysis will make a copy (and tell you), so it's more as a performance optimisation than for correctness.
Regardless of the details and extent of the borrow checking, however, it shows that it's possible in principle to infer lifetimes without explicit annotation. So, perhaps C++ could support it.
As you say, it's the semantics of the syntax that matter. I'm not familiar with C++'s compiler internals though so it could be impractical.