How to transfer ERC 721 Token to a Reach Smart Contract

[asolpshinning]

I wrote a contract in Reach to receive ERC 721, but I found out the transaction was being reverted. I researched the reason for it and discovered for any smart contract to receive ERC 721, it must implement this interface:
IERC721Receiver.onERC721Received, which is called upon a safe transfer.

Wondering if I need to, or how to write this interface in Reach as an API. If I write as an API, it says the function has to return the solidity selector, which I am not sure how to implement that in the Reach function/API...
This is how it looks in solidity:
/~https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/IERC721Receiver.sol

Is there an equivalent to the selector function in Reach ?

function onERC721Received(address, address, uint256, bytes calldata) external pure returns (bytes4) {
        return IERC721Receiver.onERC721Received.selector;
    }

Any ideas?

[jeapostrophe]

We don't support that API form right now, because we have no types like bytes (that uses unbounded space). I will work on it and reply here when I have a solution.

[asolpshinning]

Thank you Jay. Pending the time we get a solution, I would love to write the contract with solidity code and deploy it with Reach so I can use Reach backend (compiled JavaScript), to deploy and interact with the contract.
Is this possible ?
If yes, any example code I can look at?
Thanks for your help.

[jeapostrophe]

You could write it directly in Solidity, let's call that Raw, and have a Reach program interact with it, let's call that Refined, by having a remote object in Refined that is bound to Raw. For an example of doing stuff like this, check out --- /~https://github.com/reach-sh/reach-lang/tree/master/examples/remote

[willghatch]

Just FYI, BytesDyn is available now: https://docs.reach.sh/rsh/compute/#rsh_BytesDyn

So you can write an API with this signature to support receiving ERC721s: onERC721Received: Fun([Address, Address, UInt, BytesDyn], Bytes(4))