Distinct Witnesses

The distinct keyword prevents repetitions of witness indices in the program's ABI. This ensures that the witnesses being returned as public inputs are all unique.

The distinct keyword is only used for return values on program entry points (usually the main() function).

When using disctinct and pub simultaneously, distinct comes first. See the example below.

You can read more about the problem this solves here.

Example

Without the distinct keyword, the following program

fn main(x : pub Field, y : pub Field) -> pub [Field; 4] {
    let a = 1;
    let b = 1;
    [x + 1, y, a, b]
}

compiles to

{
  //...
  "abi": {
    //...
    "param_witnesses": { "x": [1], "y": [2] },
    "return_witnesses": [3, 2, 4, 4]
  }
}

Whereas (with the distinct keyword)

fn main(x : pub Field, y : pub Field) -> distinct pub [Field; 4] {
    let a = 1;
    let b = 1;
    [x + 1, y, a, b]
}

compiles to

{
  //...
  "abi": {
    //...
    "param_witnesses": { "x": [1], "y": [2] },
    //...
    "return_witnesses": [3, 4, 5, 6]
  }
}