存储槽与 Gas 优化
了解 Solidity 如何将状态变量布局到 32 字节的存储槽中，并利用这些知识编写节省 Gas 的合约。
存储槽与 Gas 优化 是 CoddyKit 上的免费 Blockchain Smart Contracts with Solidity 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Blockchain Smart Contracts with Solidity 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Blockchain Smart Contracts with Solidity 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Why Storage Costs Matter
Writing to contract storage is one of the most expensive operations on Ethereum. Understanding the storage layout lets you reduce slots written and save users real money.
The 32-Byte Slot
Contract storage is an array of slots, each 32 bytes (256 bits). State variables are assigned to slots in declaration order, starting at slot 0.
Variable Packing
Multiple small variables that fit within 32 bytes are packed into the same slot. A uint128 and another uint128 share one slot, halving storage writes if updated together.
uint128 a; // slot 0
uint128 b; // slot 0 (packed)
uint256 c; // slot 1Declaration Order Matters
Packing only works for adjacent variables that fit. Poor ordering wastes slots. Group small types together rather than interleaving them with full-size uint256 variables.
Bad vs Good Ordering
Interleaving a small type between large ones prevents packing and uses extra slots.
// Bad: 3 slots
uint128 x;
uint256 y;
uint128 z;
// Good: 2 slots
uint256 y;
uint128 x;
uint128 z;Mappings and Dynamic Arrays
Mappings and dynamic arrays do not pack. Their slot holds metadata, and actual values are stored at hashed locations. Each element write is its own storage cost.
Constants and Immutables
Values marked constant or immutable are stored in the contract bytecode, not in storage slots. Reading them is far cheaper than reading a state variable.
uint256 public constant MAX = 1000;
address public immutable owner;Caching Storage in Memory
Reading the same storage variable repeatedly inside a loop is wasteful. Cache it in a memory local variable once, operate on it, then write back once.
uint256 total = balance; // read once
for (uint i; i < n; i++) total += amounts[i];
balance = total; // write onceAvoiding Redundant Writes
Writing a value identical to the current one still costs gas. Skip a storage write if the new value equals the existing one, or only update when something actually changed.
Cheaper Storage Refunds
Clearing a storage slot back to zero gives a partial gas refund. Patterns that delete unused entries can reclaim some cost, though refund rules have changed across network upgrades.
Measuring Gas Usage
Use a gas reporter to see the cost of each function. Optimize the hottest, most-called functions first; micro-optimizing rarely-used code is not worth the readability cost.
Quick Check
Check your storage optimization knowledge.
Recap
You learned to optimize contract storage:
- Storage is 32-byte slots assigned in declaration order
- Pack small adjacent variables to share slots
- Use constant/immutable for fixed values
- Cache storage in memory, avoid redundant writes, and measure gas
Smart storage layout directly lowers the cost of using your contract.
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常见问题解答
「存储槽与 Gas 优化」课时是免费的吗？
是的 — 「存储槽与 Gas 优化」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Blockchain Smart Contracts with Solidity 课程的其余内容，请升级到 CoddyKit PRO。 Blockchain Smart Contracts with Solidity 课程共包含 4 节课。
「存储槽与 Gas 优化」这节课中我会学到什么？
了解 Solidity 如何将状态变量布局到 32 字节的存储槽中，并利用这些知识编写节省 Gas 的合约。 你通过在浏览器中直接运行的动手代码来练习 Blockchain Smart Contracts with Solidity，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Blockchain Smart Contracts with Solidity 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Blockchain Smart Contracts with Solidity 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「存储槽与 Gas 优化」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Blockchain Smart Contracts with Solidity 课中编写并运行代码吗？
能。每节 Blockchain Smart Contracts with Solidity 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。