how to change approveAndCall() function for upgraded compiler version of solidity 0.5.1 from 0.4.6?

Question

Here is the code snipped which is used when I'am working with compiler version 0.4.6 :

function approveAndCall(address _spender, uint256 _value, bytes memory _extraData) public returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        if(!_spender.call(bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))), msg.sender, _value, this, _extraData)) { 
            throw; 
        }
        return true;
    }

Now I'm compiling this code with version 0.5.1, what should I do? I've already referred Read the Docs content : v0.5.0 Breaking Changes, but really I didn't understand it.

Answer 1

I am not sure about below code may resolve your problem or not. You may try the following and let me know about the result.

 function approveAndCall(address _spender, uint256 _value, bytes memory _extraData) public returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    (bool success, bytes memory data)  = address(_spender).call(abi.encode(
        bytes4(
            bytes32(
                keccak256(
                    abi.encodePacked(
                        "receiveApproval(address,uint256,address,bytes)"
                    )
                )
            )
        ),
        msg.sender, _value, this, _extraData))
    ;
    require(success);
    return true;
}