Smart Contract Requirements and Architecture BBLC Practice Questions (Page 6)

Questions 26–30

1. 26application · medium

   A DAO treasury contract has three roles: proposers who submit spending proposals, members who vote, and an executor who can execute approved proposals. The contract must ensure that only the executor can call the executeProposal function. Which access-control design should be used?

   • AUse a role-based access control mapping that stores the executor address and a modifier to enforce it.
   • BAllow any member to execute after the voting period ends.
   • CMake the function public with no access control, relying on the frontend to hide it.
   • DUse a modifier that checks if the caller is the contract owner.
   Reveal Solution Discussion Select an answer first
2. 27application · medium · select all that apply

   A team is eliciting requirements for a smart contract that will manage a subscription service. Select all the non-functional requirements that should be documented.

   • AThe contract must allow users to subscribe, cancel, and renew their subscriptions.
   • BThe contract must minimize gas costs for subscription renewals.
   • CThe contract must store the subscription tier for each user.
   • DThe contract must be upgradeable to allow adding new features without changing the address.
   • EThe contract must be thoroughly tested before deployment to ensure it handles edge cases.
   Check answers Discussion Select an answer first
4. 28expert · hard

   A team is upgrading a smart contract using a proxy pattern. They have a storage layout with a uint256 at slot 0 and an address at slot 1. In the new implementation, they want to add a new state variable. To avoid storage collision, what should they do?

   • ADelete an existing variable and reuse its slot.
   • BAdd the new variable at the end of the existing storage layout.
   • CInsert the new variable in the middle of the existing layout.
   • DUse a separate storage contract for the new variable.
   Reveal Solution Discussion Select an answer first
5. 29application · medium

   A real-estate firm is designing a smart contract to manage rental agreements. The contract must store the landlord, tenant, monthly rent, and payment history. The architect wants to minimize gas costs for frequent payment updates. Which architecture decision best achieves this?

   • AUse a mapping from payment ID to payment details and store all historical data.
   • BStore the full payment history in a single dynamic array and append each payment record.
   • CStore each payment as a separate contract instance to isolate data.
   • DStore only the current payment status and the latest payment timestamp in state variables.
   Reveal Solution Discussion Select an answer first
6. 30foundation · easy

   In a smart contract system, what is the primary purpose of an interface that defines a function for another contract to call?

   • ATo store the contract's state
   • BTo enable inter-contract communication
   • CTo optimize gas usage
   • DTo manage the contract's upgradeability
   Reveal Solution Discussion Select an answer first