If you used it in a way that allows the closure to escape the scope, you'd get one of the "foo can't outlive bar in score ...". (On a mobile, can't write an example easily)
You can use unsafe if you want to feel like working with C :-)
There's nothing stopping you from doing things you know are correct. You just sometimes need to tell the compiler that you know better and guarantee that the code is fine.
you can have "escaping" closure. But you cannot return something that outlives it's lifetime. So the closure must own data, not merely refer to it. The online Rust book should habe the details.
