How to cast an array made up of user-defined value types to the underlying type in Solidity?

Question

I have an array which is made up of user-defined value types:

type UD60x18 is uint256;
UD60x18 memory foo[] = new UD60x18[](2);

Now, I would like to turn this into uint256. Can I cast this array to uint256[] without creating another variable?

Answer 1

To answer your comment, the following function would do that conversion using assembly :

// Since UD60x18 is uint256 their underlying size and representation are the same
// Just make a uint256[] reference point to your UD60x18[] memory variable
function unwrapArray(UD60x18[] memory foo) internal pure returns (uint256[] memory bar) {
    assembly {
        bar := foo
    }
}

Thus, this would return a uint256[] with values [1, 2] :

function test() public pure returns (uint256[] memory) {
    UD60x18[] memory foo = new UD60x18[](2);
    foo[0] = UD60x18.wrap(1);
    foo[1] = UD60x18.wrap(2);
    return unwrapArray(foo); // [1, 2]
}

It does create a new variable though... As far as I know of, there is no implicit or explicit conversion allowed for used defined value types currently.