How to Properly Change Variable Values and Use Return Functions in Solidity

Learn how to manage state changes in Solidity smart contracts by separating vote results logic into view and state-changing functions.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to change variable's value and use return as a view function in solidity

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Problem: Managing State in Solidity

When working with Solidity, a common challenge arises when you want to manipulate a variable's value while simultaneously returning a result from a function. In this case, we have a smart contract designed for voting, where users can vote for options 'a' or 'b.' The contract keeps track of votes in an array, but needs to return results based on the voting outcome.

Here's the key issue: Solidity uses view functions only for reading data without altering the state. Thus, it blocks attempts to change the vote counts while trying to return results, leading to errors in the Remix IDE.

In this guide, we’ll break down how to tackle this limitation by restructuring the code to achieve the desired functionality.

Breakdown of the Original Problem

Initially, the contract holds the following:

An array to store the votes (votes)

Functions to allow users to vote for options 'a' and 'b' (vote_a and vote_b)

And a results function (results) that should return the outcome (like "tie", "a wins", or "b wins") while resetting the votes.

Example Code Snippet

Here's what the original code looks like:

[[See Video to Reveal this Text or Code Snippet]]

Solution: Splitting the Functions

To resolve the issue while adhering to Solidity's state change rules, we can separate the functionality into two different functions:

setResults(): This function will handle the resetting of the vote counts and will only be callable by the contract owner to modify the state of the contract.

results(): This function will read the vote values and return the outcome as a string without altering the vote counts itself.

Revised Smart Contract Code

Here’s how the modified smart contract looks:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Explained

Owner Control: By introducing an owner variable and a modifier onlyOwner, we ensure that only the contract creator can reset the vote counts. This adds a layer of security to your contract.

Separation of Concerns: The results() function is strictly a view function, which reads the vote counts and returns the outcome without changing any state variables. This complies with the restrictions of Solidity's view functions.

Important Note

Before calling the results() function to check who won, always ensure that you have called setResults() first to clear the vote counts. This two-step process ensures that your contract behaves as intended.

Conclusion

By restructuring your functions into separate responsibilities, you can effectively manage state changes and return meaningful results in your Solidity smart contracts. This approach allows you to utilize the strengths of Solidity, like security and state management, without running into common pitfalls.

Feel free to implement these suggestions in your own contracts to create more efficient and safer applications!