Opposite of Borrow trait for Copy types?

Question

I\'ve seen the Borrow trait used to define functions that accept both an owned type or a reference, e.g. T or &T. The borrow

Answer 1

With the function you have you can only use a u32 or a type that can be borrowed as u32.

You can make your function more generic by using a second template argument.

fn foo>(value: N) -> T {
    *value.borrow()
}

This is however only a partial solution as it will require type annotations in some cases to work correctly.

For example, it works out of the box with usize:

let v = 0usize;
println!("{}", foo(v));

There is no problem here for the compiler to guess that foo(v) is a usize.

However, if you try foo(&v), the compiler will complain that it cannot find the right output type T because &T could implement several Borrow traits for different types. You need to explicitly specify which one you want to use as output.

let output: usize = foo(&v);