Allowing the usage of type on non-primitive types

Language Design
1

I have previously posted this request as an issue on Solc GitHub, but it has not been addressed to completion, so I’d like to bring it onto a broader discussion in this forum.

Consider this, for example:

library BigNumber {
    function add(uint256[] memory x, uint256[] memory y) internal pure returns (uint256[] memory z) { ... }
    function sub(uint256[] memory x, uint256[] memory y) internal pure returns (uint256[] memory z) { ... }
    function mul(uint256[] memory x, uint256[] memory y) internal pure returns (uint256[] memory z) { ... }
    ...
}

Since the type keyword does not support non-primitive types such as uint256[], the only alternative is to “wrap” that type inside a structure:

struct Obj {
    uint256[] data;
}

library BigNumber {
    function add(Obj memory x, Obj memory y) internal pure returns (Obj memory z) { ... }
    function sub(Obj memory x, Obj memory y) internal pure returns (Obj memory z) { ... }
    function mul(Obj memory x, Obj memory y) internal pure returns (Obj memory z) { ... }
    ...
}

However, uint256[] and struct Obj { uint256[] data; } do not share the exact same memory-layout, and ultimately, the solution above yields a higher gas cost.

So ideally, the type keyword should also support non-primitive types.