How to convert `bytes4` to `bytes memory` in Solidity?

Question

bytes4 is a commonly needed data type in Solidity, due to its use in msg.sig and, more broadly speaking, in function selectors (e.g. Contract.func.selector).

How can one convert bytes4 to bytes memory?

Answer 1

abi.encodeWithSelector can be used for this:

bytes memory a = abi.encodeWithSelector(msg.sig);
bytes memory b = abi.encodeWithSelector(Contract.func.selector);

Answer 2

You can do it directly using abi.encode() or abi.encodePacked().

function get(bytes4 _val) public pure returns(bytes memory) {
        return abi.encode(_val);
}

Example:

Input: 0x60c06040

Output: 0x60c0604000000000000000000000000000000000000000000000000000000000