SMART CONTRACTS, DEFI & WEB3 SECURITY - Chapter 2, Exercise 1 Solution
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A Transaction That Needs More Gas Than Its Own Limit

PROBLEM
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A transaction has a gas limit of 100,000, but genuinely needs 130,000
gas to fully complete. Using this chapter's own explanation of
out-of-gas behavior, describe exactly what happens to (a) the
transaction's intended state changes, and (b) the gas the sender paid
for.

SOLUTION
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(a) THE TRANSACTION'S INTENDED STATE CHANGES
Execution proceeds normally, consuming gas step by step, until it hits
the 100,000 gas limit partway through - short of the full 130,000 it
would have needed to finish. At that exact point, the EVM halts
execution and reverts every state change the transaction had attempted
to make up to that point. This chapter is specific that reverting
means ALL attempted changes are undone, not just the ones that hadn't
happened yet - so the transaction, from the outside, ends up having no
lasting effect on the contract's own state at all, exactly as if it
had never been attempted (aside from the fee, covered below).

(b) THE GAS THE SENDER PAID FOR
The gas actually consumed doing that partial work - up to the full
100,000 gas limit - is NOT refunded, even though none of the intended
state changes actually took effect. This chapter explains this is a
deliberate choice: real, genuine computational effort was spent by
every node re-executing that partial work, and refunding it would let
someone repeatedly trigger doomed, out-of-gas transactions to consume
network resources for free.

So the sender ends up in a real, specific bad outcome: they pay for
100,000 gas's worth of real computation, and get nothing for it - no
successful state change, and no refund of the gas spent getting to the
point of failure.

ANSWER: The transaction's intended state changes are fully reverted, as
if the transaction never happened - but the sender still pays for
however much gas was actually consumed before hitting the limit (up to
the full 100,000 gas limit in this case), since that computation was
genuinely performed by the network even though it ultimately failed.

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WHY THIS WORKS AS AN ANSWER

This correctly separates the two distinct outcomes the question asks
about (state changes vs. gas payment) and applies the chapter's own
specific reasoning for why the gas isn't refunded, rather than
assuming a "failed transaction, no charge" outcome that doesn't match
how the EVM actually behaves.