Design Pattern Solidity: Initialize Contract after Deployment

How to use the Initializable pattern

There are a few reasons why you might want to initialize a contract after deployment and not directly by passing constructor arguments. But first let's look at an example:

contract MyCrowdsale {
  uint256 rate;

  function initialize(uint256 _rate) public {
    rate = _rate;
  }
}

What's the advantage over constructor(uint256 _rate)?

  • Deployment and configuration does not need to happen at the same time. This can be useful when your workflow requires it.
  • Easier Etherscan verification as you do not have to deal with messy constructor arguments.
  • Can be used to avoid the 'Stack too deep, try removing local variables' error when passing more than 13 variables.
  • It allows your contracts to be upgradable.

Avoid multiple initializations

Make sure though that you do not allow multiple initializations. For just a few parameters, simply add a check for each parameter, e.g., require(rate == 0). For many parameters, add an isInitialized boolean state variable:

contract MyContract {
  bool isInitialized = false;

  function initialize(
    uint256 _param1,
    uint256 _param2,  
    uint256 _param3,
    address _param4,
    address _param5,
    bytes32 _param6,
    bytes32 _param7
  ) public {
    require(!isInitialized, 'Contract is already initialized!');
    isInitialized = true;

    param1 = _param1;
    ...
    param7 = _param7;
  }
}

Markus Waas

Solidity Developer

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