Data location in Solidity

storage persists, memory is scratch, calldata is the call.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

// Data location matters: storage persists, memory is scratch,
// calldata is the read-only bytes of the call itself.
contract LabelMaker {
    string public stored;

    function keep(string calldata label) external {
        stored = label;  // calldata copies into storage
    }

    function shout(string memory label)
        public pure returns (string memory)
    {
        return string.concat(label, "!");
    }

    function shoutStored() external view returns (string memory) {
        return shout(stored);  // storage copies into memory
    }
}

How it works

1. Assigning calldata to a state string copies into storage.
2. memory parameters are mutable scratch copies.
3. string.concat builds new memory strings.

Keywords and builtins used here

• contract
• external
• function
• public
• return
• returns
• string

The run, in numbers

Lines

22

Characters to type

551

Tokens

76

Three-star pace

55 tpm

At the three-star pace of 55 tokens a minute, this run takes about 83 seconds.

Type this snippet

Step 1 of 3 in Data & gas, step 14 of 28 in Language basics.

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