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Queue Offer

This smart contract implements a queue data structure called OfferQueue that allows efficient insertion and removal of items from both ends of the sequence. It is used to implement First-In-First-Out (FIFO) queues. The code is inspired by OpenZeppelin Contracts (last updated v4.6.0).

Usage

To use the OfferQueue data structure, follow these steps:

  1. Import the necessary library:

    import "openzeppelin-contracts/utils/math/SafeCast.sol";

  2. Define an instance of the OfferQueue struct:

    Queue.OfferQueue queue;

  3. Perform operations on the queue using the available functions.

Operations

The OfferQueue struct provides the following functions for working with the queue:

createQueueOffer

Inserts an item at the end of the queue.

function createQueueOffer(OfferQueue storage queue, Offer memory offer ) internal

front

Returns the item at the beginning of the queue.

function front(OfferQueue storage queue) internal view returns (Offer memory value)

back

Returns the item at the end of the queue.

function back(OfferQueue storage queue) internal view returns (Offer memory value)

at

Returns the item at a specified position in the queue.

function at(OfferQueue storage queue, uint256 index) internal view returns (Offer memory value)

clear

Resets the queue back to being empty.

function clear(OfferQueue storage queue) internal

length

Returns the number of items in the queue.

function length(OfferQueue storage queue) public view returns (uint256)

isEmpty

Returns true if the queue is empty.

function isEmpty(OfferQueue storage queue) public view returns (bool)

getQueue

Returns an array containing all the offers in the queue.

function getQueue(OfferQueue storage queue) public view returns (Offer[] memory)

Custom Types

The OfferQueue struct contains the following custom type:

struct Offer {
    uint creatorId;
    address token;
    uint256 amount;
    uint256 timestamp;
    address owner;
}

This struct represents an offer and contains the following fields:

  • creatorId: The ID of the offer creator.
  • token: The address of the token associated with the offer.
  • amount: The amount of the offer.
  • timestamp: The timestamp of the offer creation.
  • owner: The address of the offer owner.

Events

The OfferQueue struct emits the following events:

  • OfferCreated: Fired when a new offer is created.
  • OfferTaken: Fired when an offer is taken from the queue.
  • OfferModified: Fired when an offer in the queue is modified.

Notes

  • The OfferQueue data structure can only be used in storage and not in memory.
  • All operations on the queue have a constant time complexity of O(1).
  • When using the clear function, note that the current items are left behind in storage, which may affect potential gas refunds.

This library was made available since version 4.6 of OpenZeppelin Contracts.