Design Pattern Solidity: Stages
How you can design stages in your contract
Closely related to the concept of finite-state machines, this pattern will help you restrict functions in your contract. You will find a lot of situations where it might be useful. Any time a contract should allow function calls only in certain stages.
Let's look at an example:
contract Pool {
enum Stages {
Initialize,
Contribute,
Collect,
}
Stages public stage = Stages.Initialize;
modifier atStage(Stages _stage) {
require(
stage == _stage,
"Wrong pooling stage. Action not allowed."
);
_;
}
function init(...) external atStage(Stages.Initialize) {
...
currentStage = Stages.Contribute;
}
function contribute(...) external atStage(Stages.Contribute) {
...
if (hasContributionThresholdReached) {
currentStage = Stages.Collect;
}
}
function collect(...) external atStage(Stages.Collect) { }
}The pooling contract has three stages:
- The administrator has to set the parameters using
init(). - Users contribute funds to the pool using
contribute(). - Once sufficient funds are collected, the pool automatically goes into the last stage which then allows users to receive their share of whatever was purchased by the contract using
collect().
The staging system keeps a clear separation and access control of functions. Further, having a public stage variable makes it clear for the user as well.
Markus Waas
Solidity Developer