Solidity Assembly

Simple Example

pragma solidity ^0.8.0;

contract Simple {
    constructor(address _addr) {
        assembly {
            // Get the size of the code
            let size := extcodesize(_addr);
            // Allocate output byte array
            code := mload(0x40);
            // New "memory end" including padding
            mstore(0x40, add(code, and(add(add(size, 0x20), 0x1f), not(0x1f))));
            // Store length in memory
            mstore(code, size);
            // Retrieve the code
            extcodecopy(addr, add(code, 0x20), 0, size);
        }
    }
}

From Opcode

pragma solidity ^0.8.0;

contract Opcode {
  constructor() {
        address myContract;
    bytes memory opcode = "\x60\x0a\x60\x0c\x60\x00\x39\x60\x0a\x60\x00\xf3\x60\x2a\x60\x80\x52\x60\x20\x60\x80\xf3";

    assembly {
        myContract := create(0, add(opcode, 0x20), mload(opcode))
    }

    // Some code here...
  }
}