You can pretty well see by grepping whether it's going to create a dangling reference or not. For example, in C++ codebases I'm most familiar with, anything th

You can pretty well see by grepping whether it's going to create a dangling reference or not. For example, in C++ codebases I'm most familiar with, anything that takes a const foo& isn't going to retain a reference, and for unfamiliar stuff that takes a const foo* or foo*, you can look at the outputs, which, if it's a P<Expr>, all you need is the institutional knowledge that Exprs don't have dangling references. You don't need to debate with me the merits of replacing visual analysis with sound analysis. (If I have a negative opinion of Rust on the matter, it's that it's not good enough at that.) My beef here is with the way the blog article overstates the case, saying you just wouldn't do this sort of thing or this specific thing. You so would make temporary references deep into an AST while expanding derived implementations.