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  • Difficulty - Medium
    Total Plays - 15
    Allowed Time - 10 sec
    Best time - 4.554

    What makes nested delegatecalls dangerous?

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    Explanation:
    Each delegatecall runs in the caller’s storage space, so nesting them multiplies the chances of overwriting incorrect slots. This breaks upgradeability guarantees and corrupts state. Auditors treat deep delegatecall chains as red flags.
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  • Difficulty - Medium
    Total Plays - 18
    Allowed Time - 10 sec
    Best time - 2.746

    Why do upgradeable contracts avoid constructors?

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    Explanation:
    Constructors run only during deployment and do not execute through proxies. Using an initializer ensures state is properly set through proxy calls. The entire proxy pattern relies on replacing constructors with explicit initialization.
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  • Difficulty - Medium
    Total Plays - 22
    Allowed Time - 10 sec
    Best time - 1.062

    Why avoid multiple SSTOREs in a function?

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    Explanation:
    SSTORE is one of the most expensive operations and repeating it unnecessarily multiplies costs. Caching values into memory and writing once dramatically optimizes gas. This is foundational in gas-sensitive protocols.
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  • Difficulty - Medium
    Total Plays - 19
    Allowed Time - 10 sec
    Best time - 1.746

    Why is assert() dangerous in production?

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    Explanation:
    assert() triggers a Panic error and is intended only for internal guarantees. If it fires in production, it indicates a compiler or logic bug. Developers should use require() for user-facing validation.
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  • Difficulty - Medium
    Total Plays - 14
    Allowed Time - 10 sec
    Best time - 6.381

    What does a selector collision indicate?

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    Explanation:
    Selector collisions occur when different function signatures hash to the same first 4 bytes. This leads to unintended dispatching and silent bugs. It’s especially dangerous in diamond proxies and minimal routers.
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  • Difficulty - Medium
    Total Plays - 18
    Allowed Time - 10 sec
    Best time - 1.487

    Why is msg.value validation kept at the top of functions?

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    Explanation:
    Validating msg.value early ensures no state mutation occurs before detecting invalid ether transfers. This prevents partially updated storage on failure, preserving atomicity. It aligns with checks-effects-interactions
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  • Difficulty - Medium
    Total Plays - 10
    Allowed Time - 10 sec
    Best time - 1.153

    What makes fallback functions error-prone?

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    Explanation:
    Fallbacks receive raw calldata without predefined structure, forcing developers to manually decode and validate inputs. Any mistake leads to reentrancy or mis-routing. They must be extremely minimal.
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  • Difficulty - Medium
    Total Plays - 15
    Allowed Time - 10 sec
    Best time - 4.927

    Why do storage reads cost more than memory reads?

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    Explanation:
    Storage accesses require Merkle-Patricia proof validation at the state level. This makes SLOAD one of the most expensive operations in Solidity. Caching values into memory significantly reduces repeated cost.
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  • Difficulty - Medium
    Total Plays - 8
    Allowed Time - 10 sec
    Best time - 6.303

    Why are external loops discouraged?

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    Explanation:
    Unbounded loops that depend on storage or user-controlled arrays can exhaust gas and render functions uncallable. Attackers can intentionally cause denial-of-service through loop amplification. Good design avoids external iteration
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  • Difficulty - Medium
    Total Plays - 8
    Allowed Time - 10 sec
    Best time - 2.699

    Why avoid comparing strings on-chain?

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    Explanation:
    String comparison requires hashing or byte-by-byte checks, both of which are expensive in the EVM model. It also introduces risk when mixed with packed encodings. Developers instead rely on enums or hashed IDs.
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  • Difficulty - Medium
    Total Plays - 9
    Allowed Time - 10 sec
    Best time - 7.363 sec

    What makes memory expansion expensive?

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    Explanation:
    Memory follows a quadratic cost function, meaning costs rise rapidly as the memory footprint grows. Careless array allocations can suddenly inflate execution cost. This is a frequent root cause of gas blowups in audits.
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  • Difficulty - Medium
    Total Plays - 10
    Allowed Time - 10 sec
    Best time - 2.358

    Why is PUSH0 useful in gas optimization?

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    Explanation:
    PUSH0 provides a zero literal without consuming calldata or memory. This reduces bytecode size and simplifies stack management. It's extremely helpful in tight loops and assembly-heavy contracts.
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  • Difficulty - Medium
    Total Plays - 7
    Allowed Time - 10 sec
    Best time - 10

    What does “state shadowing” indicate in inheritance?

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    Explanation:
    State shadowing happens when a derived contract redeclares a state variable with the same name as a parent. This creates storage misalignment and unexpected slot overwrites. Auditors treat this as a major upgradeability and correctness risk.
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  • Difficulty - Medium
    Total Plays - 7
    Allowed Time - 10 sec
    Best time - 2.234

    Why is calldata preferred for router functions?

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    Explanation:
    Calldata avoids copying user inputs into memory, significantly reducing gas usage for large payloads. Router contracts receive untrusted inputs, so avoiding memory expansion is both cheaper and safer. This is why AMMs and DEX routers heavily rely on calldata
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  • Difficulty - Medium
    Total Plays - 6
    Allowed Time - 10 sec
    Best time - 3.026

    Why do auditors flag “silent reverts”?

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    Explanation:
    Silent reverts hide failure reasons, making debugging and validation difficult. They also open the door for inconsistent execution paths
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  • Difficulty - Medium
    Total Plays - 8
    Allowed Time - 10 sec
    Best time - 2.492

    What does REVERT preserve that INVALID does not?

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    Explanation:
    REVERT allows returning structured revert data back to the caller, which improves debugging and interface guarantees. INVALID terminates execution with no return payload. This distinction is crucial for protocols relying on bubble-up error messaging.
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  • Difficulty - Medium
    Total Plays - 7
    Allowed Time - 10 sec
    Best time - 3.912

    Which op is used for external code size?

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    Explanation:
    EXTCODESIZE checks if the target has code deployed. It helps detect contracts vs EOAs in validation logic
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