Contract Structure & Versions

Code License

• Specify a license at the top of every file.

// SPDX-License-Identifier: MIT

Solidity Versions

pragma solidity 0.8.7;              // A specific version
pragma solidity ^0.8.7;             // Version 0.8.7 or higher
pragma solidity >=0.8.7 <0.9.0;     // Only versions including or greater than 0.8.7 
                                    // and less than 0.9.0

Contract Template

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract HelloWorld {
}

Import

• When you have multiple files and you want to import one file into another, Solidity uses the importkeyword:

import "./someothercontract.sol";

contract newContract is SomeOtherContract {
}

• So if we had a file named someothercontract.sol in the same directory as this contract (that's what the ./means), it would get imported by the compiler.

• Imports can also be renamed when being imported:

import {WETH9Test as Handler} from "./WETH9Test.t.sol";

contract WETH9TestInvariant is Test, Counter {

    Handler public handler;

    function setUp() public {
        handler = new Handler();
    }
}

Contract Layout

• license

• version

• imports

• errors

• interfaces, libraries, contracts

• type declarations

• state variables

• events

• modifiers

• functions

Function Layout

• constructor

• receive function (if exists)

• fallback function (if exists)

• external

• public

• internal

• private

• view & pure functions