¿Cómo se manejan las tuplas para el selector de funciones?

Se usa (type1,type2,...)para representar estructuras.

Por ejemplo, la fillOrderfunción en 0x 2.0 :

function fillOrder(
    Order memory order,
    uint256 takerAssetFillAmount,
    bytes memory signature
)
    public
    returns (LibFillResults.FillResults memory fillResults);

struct Order {
    address makerAddress;           // Address that created the order.      
    address takerAddress;           // Address that is allowed to fill the order. If set to 0, any address is allowed to fill the order.          
    address feeRecipientAddress;    // Address that will recieve fees when order is filled.      
    address senderAddress;          // Address that is allowed to call Exchange contract methods that affect this order. If set to 0, any address is allowed to call these methods.
    uint256 makerAssetAmount;       // Amount of makerAsset being offered by maker. Must be greater than 0.        
    uint256 takerAssetAmount;       // Amount of takerAsset being bid on by maker. Must be greater than 0.        
    uint256 makerFee;               // Amount of ZRX paid to feeRecipient by maker when order is filled. If set to 0, no transfer of ZRX from maker to feeRecipient will be attempted.
    uint256 takerFee;               // Amount of ZRX paid to feeRecipient by taker when order is filled. If set to 0, no transfer of ZRX from taker to feeRecipient will be attempted.
    uint256 expirationTimeSeconds;  // Timestamp in seconds at which order expires.          
    uint256 salt;                   // Arbitrary number to facilitate uniqueness of the order's hash.     
    bytes makerAssetData;           // Encoded data that can be decoded by a specified proxy contract when transferring makerAsset. The last byte references the id of this proxy.
    bytes takerAssetData;           // Encoded data that can be decoded by a specified proxy contract when transferring takerAsset. The last byte references the id of this proxy.
}

El selector de función se calcula usando:

fillOrder((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),uint256,bytes)

Esto produce un keccak256 de: b4be83d519a652e54a6073d7e55643f575508112b09dcc74264b807477b576c5, y los primeros 4 bytes son:b4be83d5

Puede confirmar esto mirando este tx que llamó a fillOrder: https://etherscan.io/tx/0x4811b7492bd845a46a052b063f943c4760174e932cb171ca25a934de6e7e4da4