Is there any way to return a reference to a variable created in a function?

Question

I want to write a program that will write a file in 2 steps. It is likely that the file may not exist before the program is run. The filename is fixed.

The problem i

Answer 1

Is there any way to return a reference from a function without arguments?

No (except references to static values, but those aren't helpful here).

However, you might want to look at OpenOptions::create. If you change your first line in main to

let  f = OpenOptions::new().write(true).create(true).open(b"foo.txt");

the file will be created if it does not yet exist, which should solve your original problem.