solidity assert for several not nulls

Question

I have the following function in solidity:

function registerStudentEvaluation(string memory _firstName, string memory _lastName, string memory _subject, uint _note) public returns(Note memory) {
        bytes32 studentHash = keccak256(abi.encodePacked(_firstName, _lastName));
        bytes32 subjectHash = keccak256(abi.encode(_subject));
        address teacherAddress = msg.sender;

        assert (students[studentHash] && subjects[subjectHash] && teachers[msg.sender]);

        Note memory newNote = Note(studentHash, subjectHash, msg.sender, _note);
        bytes32 noteHash = keccak256(abi.encodePacked(studentHash, subjectHash, msg.sender, _note));
        notes[noteHash] = newNote;

        emit student_evaluated(noteHash);

        return newNote;
    }

And I am getting these errors:

TypeError: Operator & not compatible with types struct Notes.Student storage ref and struct Notes.Subject storage ref
--> notes.sol:71:17:
|
71 | assert (students[studentHash] & subjects[subjectHash] & teachers[msg.sender])

TypeError: Operator && not compatible with types struct Notes.Student storage ref and struct Notes.Teacher storage ref

TypeError: Invalid type for argument in function call. Invalid implicit conversion from struct Notes.Student storage ref to bool requested.

How can I assert for several not nulls in Solidity?

Answer 1

Solidity uses two ampersands && as the logical AND operator.

assert(true && true);

One ampersand & is the bitwise AND operator.

uint8 three = 3;                // 00000011
uint8 five = 5;                 // 00000101
uint8 result = three & five;    // 00000001

Docs: https://docs.soliditylang.org/en/v0.8.12/cheatsheet.html

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Solution: Use logical operators in the assert() condition.

assert (students[studentHash] && subjects[subjectHash] && teachers[msg.sender]);

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Note: It's not defined in your question but I'm assuming that the students property is defined as mapping(bytes32 => bool) students;