Storage vs Memory
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Storage vs Memory adalah pelajaran Web3 & DApp Development Fundamentals gratis di CoddyKit. Ini adalah pelajaran 3 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Web3 & DApp Development Fundamentals, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Web3 & DApp Development Fundamentals mencakup 4 pelajaran total.
Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.
Why Data Location Matters
In Solidity, reference types must specify a data location. The three locations are storage, memory, and calldata.
Choosing the right one affects persistence, mutability, and most importantly gas cost.
Storage
Storage is the contract's permanent on-chain state. State variables live here, and writing to storage is the most expensive operation.
Data in storage persists between transactions.
<code>contract Bank {
uint256 public total; // lives in storage forever
function add(uint256 v) public {
total += v; // writes to storage (expensive)
}
}</code>Memory
Memory is a temporary scratchpad that exists only during a function call. It is much cheaper than storage and is cleared when the function returns.
Use memory for intermediate calculations and data you do not need to persist.
<code>function build() public pure returns (uint[] memory) {
uint[] memory temp = new uint[](3);
temp[0] = 1;
temp[1] = 2;
return temp; // discarded after call
}</code>Calldata
Calldata is a read-only, non-modifiable location holding function arguments for external calls. It is the cheapest option because nothing is copied.
Use it for function parameters you only need to read.
<code>function sum(uint[] calldata values) external pure returns (uint total) {
for (uint i = 0; i < values.length; i++) {
total += values[i];
}
}</code>Storage Pointer to State
Inside a function, a storage local variable is a pointer to existing state. Modifying it changes the contract's actual storage.
<code>struct User { uint balance; }
mapping(address => User) users;
function credit() public {
User storage u = users[msg.sender];
u.balance += 100; // updates real state
}</code>Memory Copy of State
If you instead load state into a memory variable, you get an independent copy. Changes to the copy do NOT update the contract's storage.
This is a common source of bugs for beginners.
<code>function noEffect() public view returns (uint) {
User memory u = users[msg.sender];
u.balance += 100; // only the copy changes
return u.balance; // storage is untouched
}</code>Gas Cost Comparison
The cost ranking, from cheapest to most expensive:
- calldata - read-only external args, no copy
- memory - temporary, copied into RAM
- storage - persistent on-chain, very costly to write
A fresh storage write (zero to non-zero) is one of the priciest EVM operations.
Prefer calldata for external
For external functions whose array or struct parameters are only read, use calldata instead of memory to avoid an unnecessary copy and save gas.
<code>// Cheaper: no copy is made
function process(bytes calldata data) external {
// read data directly
}</code>Where Defaults Apply
State variables are always storage. Function parameters and locals of reference type must declare a location explicitly. Value types and mapping members default to storage rules automatically.
Local mappings must always be storage - they cannot live in memory.
<code>// mapping locals must be storage
function f() public {
// mapping(...) memory m; // ERROR
}</code>Caching Storage Reads
A gas optimization: if you read the same storage variable multiple times, copy it into a memory local once. Each storage read (SLOAD) costs gas.
<code>function loop() public view returns (uint) {
uint cached = total; // one SLOAD
uint acc;
for (uint i = 0; i < 10; i++) {
acc += cached; // reads memory, cheap
}
return acc;
}</code>Returning Memory
Functions that build and return new arrays or structs use memory for the return value, since storage cannot be returned by value and calldata is input-only.
<code>function pair(uint a, uint b) public pure returns (uint[] memory) {
uint[] memory out = new uint[](2);
out[0] = a;
out[1] = b;
return out;
}</code>Quick Check
Test your understanding of data locations.
Recap
You learned how Solidity data locations work:
- storage - persistent, on-chain, most expensive to write
- memory - temporary scratchpad, copied, cleared after the call
- calldata - read-only external args, cheapest, no copy
Use storage references to mutate state, memory for temporary work, and calldata for read-only external inputs to save gas.
Pertanyaan yang Sering Diajukan
Apakah pelajaran “Storage vs Memory” gratis?
Ya — teks lengkap “Storage vs Memory” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Web3 & DApp Development Fundamentals, upgrade ke CoddyKit PRO. Kursus Web3 & DApp Development Fundamentals mencakup 4 pelajaran total.
Apa yang akan aku pelajari di “Storage vs Memory”?
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Semua pelajaran dalam kursus ini
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