Some common functions
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
// ...
}
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 (see Structs in types section).
// 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
}