Deploy contract from contract in Solidity

Question

It's a common pattern to use a hub/factory contract to create multiple instances of a standard contract.

It's also common to require a way to enumerate the addresses of the created contracts.

Is there a simple minimal example of a good approach?

Answer 1

Here's a simple hub (Bakery) that deploys contracts (Cookie) from a template and keeps track of the contracts created.

Note that Cookie is part of the source file so Bakery can "see it" during compilation. Cookie's ByteCode will become part of Bakery so the new Cookie() invocation knows what to do.

Deploy the hub/factory (Bakery). It's not necessary to deploy the template (Cookie). You can create as many of the latter as needed by calling a function in the former.

pragma solidity ^0.4.8;

contract Bakery {

  // index of created contracts

  address[] public contracts;

  // useful to know the row count in contracts index

  function getContractCount() 
    public
    constant
    returns(uint contractCount)
  {
    return contracts.length;
  }

  // deploy a new contract

  function newCookie()
    public
    returns(address newContract)
  {
    Cookie c = new Cookie();
    contracts.push(c);
    return c;
  }
}


contract Cookie {

  // suppose the deployed contract has a purpose

  function getFlavor()
    public
    constant
    returns (string flavor)
  {
    return "mmm ... chocolate chip";
  }    
}

If you need more functionality in the index (e.g. is 0x123 a contract?) consider more feature-complete storage patterns: Are there well-solved and simple storage patterns for Solidity?

Hope it helps.

Answer 2

For accessing the method I created a new function and did it like this

function getCookieFlavor(address cookie) public view returns(string){
    return Cookie(cookie).getFlavor();
}

just pass in the address of the cookie which is already created.