Blockchain Developer Certification Practice

Can a function that modifies contract data also return data?

1. Yes, but only in certain cases.

2. No, it cannot return data.

3. Yes, it can return a log.

4. Yes, it returns a transaction ID.

The correct answer is: No, it cannot return data.

A function in a smart contract that modifies contract data can indeed return data, as this is a common behavior in programming. In the context of smart contracts, especially in Ethereum, functions can be designed to perform state changes (i.e., modifying contract data) while also returning values. For instance, a function that updates a balance can also return the new balance post-update. This dual capability enhances the functionality of smart contracts by allowing contracts to provide information alongside performing state modifications, which is useful for developers and users alike. Moreover, the concept of returning a log or a transaction ID does not align with the primary function of returning data. While events can be emitted for logging purposes, and transaction IDs can be provided as a side effect of a transaction, these are not direct returns of the function in question. Return values from functions should ideally give back the computed result or status derived from executing the function, rather than relying on side effects. In conclusion, the ability for a function to modify contract data and simultaneously return data enriches the usability and effectiveness of smart contracts, providing real-time feedback to users after an operation is performed.