# Rust lang. ## Topic A You have implied a function which works well for a while (suppose A is a known struct in your project): ```rust fn foo(a: &[A]) -> usize ``` One day your colleague complain that “I need to call your foo but I have only a ref. of A in my context, how should I do?” Please refine the definition of your foo function without breaking any other code in the project, and enable someone calling your foo with single reference of A (`&A`)