솔리디티 Contract 구조

solidity v0.8.14 기준 문법

State Variables

State variables are variables whose values are permanently stored in contract storage.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.0 <0.9.0;

contract SimpleStorage {
    uint storedData; // State variable
    // ...
}

Functions

Functions are the executable units of code. Functions are usually defined inside a contract, but they can also be defined outside of contracts.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.1 <0.9.0;

contract SimpleAuction {
    function bid() public payable { // Function
        // ...
    }
}

// Helper function defined outside of a contract
function helper(uint x) pure returns (uint) {
    return x * 2;
}

Function Modifiers

Function modifiers can be used to amend the semantics of functions in a declarative way

Overloading, that is, having the same modifier name with different parameters, is not possible.

Like functions, modifiers can be overridden.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.22 <0.9.0;

contract Purchase {
    address public seller;

    modifier onlySeller() { // Modifier
        require(
            msg.sender == seller,
            "Only seller can call this."
        );
        _;
    }

    function abort() public view onlySeller { // Modifier usage
        // ...
    }
}

Events

Events are convenience interfaces with the EVM logging facilities.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.21 <0.9.0;

contract SimpleAuction {
    event HighestBidIncreased(address bidder, uint amount); // Event

    function bid() public payable {
        // ...
        emit HighestBidIncreased(msg.sender, msg.value); // Triggering event
    }
}

Errors

Errors allow you to define descriptive names and data for failure situations. Errors can be used in revert statements. In comparison to string descriptions, errors are much cheaper and allow you to encode additional data. You can use NatSpec to describe the error to the user.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.4;

/// Not enough funds for transfer. Requested `requested`,
/// but only `available` available.
error NotEnoughFunds(uint requested, uint available);

contract Token {
    mapping(address => uint) balances;
    function transfer(address to, uint amount) public {
        uint balance = balances[msg.sender];
        if (balance < amount)
            revert NotEnoughFunds(amount, balance);
        balances[msg.sender] -= amount;
        balances[to] += amount;
        // ...
    }
}

Struct Types

Structs are custom defined types that can group several variables.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.0 <0.9.0;

contract Ballot {
    struct Voter { // Struct
        uint weight;
        bool voted;
        address delegate;
        uint vote;
    }
}

Enum Types

Enums can be used to create custom types with a finite set of ‘constant values’.

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.0 <0.9.0;

contract Purchase {
    enum State { Created, Locked, Inactive } // Enum
}