Generic Bounds

In the Limitations section, we explained that operators are overloaded to work with references and non-references.

If you wish to write generic functions which use operators with mixed reference and non-reference, it might get tricky at first to specify the trait bounds. This page should serve as a cookbook to help you.

operation	trait bound
T $op T	T: $Op<T, Output=T>
T $op &T	T: for<'a> $Op<&'a T, Output=T>
&T $op T	for<'a> &'a T: $Op<T, Output=T>
&T $op &T	for<'a> &'a T: $Op<&'a T, Output=T>

The for<'a> syntax is something called Higher-Rank Trait Bounds, often shortened as HRTB

Example

use core::ops::Add;

/// This function can be called with both FHE types and native types
fn compute_stuff<T>(a: T, b: T) -> T
where T: Add<T, Output=T>,
      T: for <'a> Add<&'a T, Output=T>,
      for <'a> &'a T: Add<T, Output=T> + Add<&'a T, Output=T>
{
    let c = &a + &b;

    c + &b
}


fn main() {
    let result = compute_stuff(0u32, 1u32);
    println!("result: {}", result);
}