Is it possible to call contract that has no function?

Question

For example I have a contract that has the following bytecode 0x433d52593df3 (contract that returns the current block number if called). How could I call such a contract?

Answer 1

Yes, you can; send a standard transaction to it.

Solidity compiles functions/methods into a custom switch/case pattern applied to the calldata sent to the smart contract with the tx. Following that rule is not mandatory, just a best practice.

If you want to experiment your functionless smart contract using Solidity/Yul, you can start with something like this:

// SPDX-License-Identifier: MIT
pragma solidity >=0.7.0 <0.9.0;

contract ReturnBlockNumber {
    fallback() external {
        assembly {
            mstore(0x0, number())
            return(0x0, 32)
        }
    }
}

You can also use Remix to call that contract, check the Low Level Interaction panel.

Side note about 0x433d52593df3: really clever use of 3d instead of 6000 ;)