mvx_cache_patterns_skill

Overview

This skill documents drop-based write-back cache patterns for MultiversX smart contracts to reduce gas costs when endpoints read multiple storage values. It provides a minimal, safe pattern that loads storage into an in-memory struct, mutates it during execution, and commits only on scope exit. The patterns include computed helper methods and selective write-back to avoid unnecessary storage writes.

How this skill works

On entry, the cache struct reads multiple storage entries into memory. Mutations happen on the in-memory fields. A Drop implementation writes changed fields back to storage when the cache goes out of scope, making intermediate reads free and reducing round-trip storage operations. Read-only variants skip Drop, and manual scoping is used to avoid crossing async boundaries.

When to use it

• Endpoint reads 3 or more storage values in a single transaction
• Complex mutative flows where many intermediate reads occur
• View functions that read multiple values (use read-only cache without Drop)
• When you want to minimize storage writes by committing only at the end
• Before making async calls: ensure cache is dropped manually

Best practices

• Only include fields that will be mutated in Drop; skip immutable config to save gas
• Wrap cache usage in a limited scope so Drop always runs before async exits
• Provide computed helper methods on the cache to derive values without extra storage reads
• Explicitly document which fields are committed and which are read-only
• Write tests verifying Drop commits expected fields and that no fields are forgotten

Example use cases

• A deposit endpoint that reads total_shares, total_deposited, and user_balance and updates all three
• A liquidation flow that needs multiple storage lookups and heavy intermediate math across entries
• A view endpoint that computes exchange_rate from cached totals without committing anything
• A batch update handler that aggregates many changes then writes back a small set of storage keys
• Pre-async transfer logic: update balances, drop cache, then perform async external call