Modifiers in Solidity

Wrap a function; _ marks where the body runs.

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

// A modifier wraps a function; _ marks where the body runs.
contract ToolShed {
    address public steward;
    uint256 public toolsOut;

    constructor() {
        steward = msg.sender;
    }

    modifier onlySteward() {
        require(msg.sender == steward, "steward only");
        _;
    }

    function lend() external onlySteward {
        toolsOut += 1;
    }
}

How it works

1. modifier onlySteward centralizes the permission check.
2. The _; line is where the guarded body executes.
3. external onlySteward applies it at the signature.

Keywords and builtins used here

• address
• constructor
• contract
• external
• function
• modifier
• public
• require
• uint256

The run, in numbers

Lines

21

Characters to type

366

Tokens

58

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 58 seconds.

Type this snippet

Step 2 of 3 in Guards, step 9 of 28 in Language basics.

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