[SLK-01C] Inefficient `mapping` Lookups

[lucasfernandes]

SLK-01C: Inefficient mapping Lookups

Type	Severity	Location
Gas Optimization		SamLock.sol:L79, L83, L134, L136

Description:

The linked statements perform key-based lookup operations on mapping declarations from storage multiple times for the same key redundantly.

Example:

ISamLock.LockInfo memory lockInfo = lockings[wallet][lockIndex];
if (block.timestamp < lockInfo.unlockTime) revert ISamLock.SamLock__Cannot_Unlock_Before_Period();
if (amount > lockInfo.lockedAmount - lockInfo.withdrawnAmount) revert ISamLock.SamLock__InsufficientAmount();

lockings[wallet][lockIndex].withdrawnAmount += amount;

Recommendation:

As the lookups internally perform an expensive keccak256 operation, we advise the lookups to be cached wherever possible to a single local declaration that either holds the value of the mapping in case of primitive types or holds a storage pointer to the struct contained.

As the compiler's optimizations may take care of these caching operations automatically at-times, we advise the optimization to be selectively applied, tested, and then fully adopted to ensure that the proposed caching model indeed leads to a reduction in gas costs.

[lucasfernandes]

This issue was fixed at the #7 issue.