Cannot push to array in a struct

[LucasSte]

This contract:

contract Foo {
	struct My {
		bytes bb;
	}
	function bar() public pure returns (uint32) {
		My s;
		s.bb.push(2);
		return s.bb.length;
	}
}

causes this error:

thread 'main' panicked at 'not an array', src/sema/types.rs:1415:18

[Shiva953]

bb declared with bytes is a dynamic byte array and it doesn't have a push method like arrays in some other programming languages. To do that, you gotta manage the length of the array manually and use memory allocation functions.

1. Declare s as a memory variable. This would allow you to modify data(array in this case) inside of the bar function as it is declared as pure. It aligns with the function's read-only nature and preventing errors related to modifying storage in a read-only context.
2. Initialize the bytes array s.bb using new bytes(0).

pragma solidity ^0.8.0;

contract Foo {
    struct My {
        bytes bb;
    }

    function bar() public pure returns (uint256) {
        My memory s; //declare s as a memory variable
        s.bb = new bytes(0); // Initialize the bytes array
        s.bb.push(0x02);

        return s.bb.length;
    }
}

[LucasSte]

Thanks @Shiva953, you are right. solc does not allow us to push to a bytes array that is not in memory. The bug, however, still exists. The compiler must not panic because we are trying to build incorrect code. It should raise an error.

[Shiva953]

yeah sire, that's a solidity compiler limitation and I honestly don't have the slightest of the clues about anything related to compilers

[seanyoung]

Solang does support push/pop on memory arrays, even if solc does not. However, it should not panic.