---
# System prepended metadata

title: Rust lang.

---

# 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`)

