UnifiPair.sol

Primary Uses - UnifiPair.sol is responsible for many of the functionalities of liquidity pool tokens and UP tokens. First, it is responsible for the issuing and burning of Liquidity Pool Tokens (uTokens). In addition, it allows for direct reads of the reserves and ratio of the liquidity pool, as well as swaps. Lastly, it is where UP claims are processed.

uTrade V2 Pair Code / Interfaces

uTrade V2 Pair (Solidity)
uTrade V2 Pair Interface as JSON	Link Here
uTrade V2 Pair as Typescript	Link Here
Import statement codeblock (when available)

uTrade V2 Pair Contract Addresses

Each uTrade V2 Liquidity Pool uses the uTrade V2 XRC20 Interface in the contract. An example would be 0xBd99494A8EEa8425F5B83D7608b1b198763a97F8 (Link) for the WIOTX / UPIotx pair on the IoTeX Main Net.

Events

Mint

event Mint(address indexed sender, uint amount0, uint amount1);

The Mint event is emitted any time liquidity tokens are created via the mint function. In other words, when a user adds liquidity to a pair, then they will receive LP tokens, therefore the Mint event will be emitted.

Burn

event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);

The Burn event is emitted any time liquidity tokens are burned via the burn function. In other words, when a user removes liquidity from a pair, their LP tokens will be burned, therefore the Burn event will be emitted.

Swap

event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
 );

The Swap event is emitted any time the swap function is used. Under the hood, all trades on uTrade V2 are swaps. Therefore, any time somebody trades on the pair, the uTrade contract for that pair will emit a Swap event.

Sync

event Sync(uint112 reserve0, uint112 reserve1);

The Sync event is emitted anytime a function occurs that may change the reserves of a token pair. In other words, anytime the amount of the two tokens within a liquidity pool may change. Therefore, whenever amint, burn, swap, or sync function is called, the Sync event will be emitted.

Read-Only Functions

MINIMUM_LIQUIDITY

function MINIMUM_LIQUIDITY() external pure returns (uint);

The MINIMUM_LIQUIDITYfunction will always return 1000. The function itself refers to the burning of initial LP tokens that occurs once when a pool is created. This burn of a tiny amount allows for cleaner LP token numbers therefore avoiding LP tokens being represented as very small decimals value. This allows the tick size to be more precise and prevents rounding errors.

factory

function factory() external view returns (address);

The factory function will return the current factory address for uTrade V2.

WBNB

function WETH() external view returns (address);

The WETHfunction will return the address of WIOTX on IoTeX. As this does not change, it will always return 0xa00744882684c3e4747faefd68d283ea44099d03.

token0

function token0() external view returns (address);

The token0 function will return the contract address of the first token that makes up the liquidity pair. In other words, if the liquidity pool is made up of USDT / USDC, it will return the contract address of USDT.

token1

function token1() external view returns (address);

The token1 function will return the contract address of the first token that makes up the liquidity pair. In other words, if the liquidity pool is made up of USDT / USDC, it will return the contract address of USDC.

getReserves

function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);

The getReserves function returns the reserves of the two tokens that make up the liquidity pool as reserve0 and reserve1. These two values can be helpful in determining the current price of each asset. The function also returns a timestamp with the block number.

price0CumulativeLast

function price0CumulativeLast() external view returns (uint);

The price0CumulativeLastfunction is for Oracle usage on uTrade V2. The value of token0 is captured at the end of each block, and can be called using this function to feed into an Oracle to determine a more time-weighted 'average' price.

price1CumulativeLast

function price1CumulativeLast() external view returns (uint);

The price1CumulativeLast function is for Oracle usage on uTrade V2. The value of token1 is captured at the end of each block, and can be called using this function to feed into an Oracle to determine a more time-weighted 'average' price.

kLast

function kLast() external view returns (uint);

The kLast function returns the value of reserve0 * reserve1, after any event that may have triggered a change in the liquidity. For example, the execution of a swap function or a mint function.

State-Changing Functions

mint

function mint(address to) external returns (uint liquidity);

The mint function creates the LP tokens that represent a user's tokens in a liquidity pool. For example, if a user provides 20,000 IOTX and 2000 USDT liquidity to a pool, the Unifi Pair Smart Contract will mint an amount of uUSDT tokens. Will emit the Mint, Sync, and Transfer events.

burn

function burn(address to) external returns (uint amount0, uint amount1);

The burn function destroys the LP tokens that represent a user's token in a liquidity pool. For example, if a user removes 20,000 IOTX and 2000 USDT liquidity to a pool, the Unifi Pair Smart Contract will burn an amount of uUSDT tokens. Will emit the Burn, Sync, and Transfer events.

claimUP

function claimUP(address to) external lock returns(uint) {

The claimUP function claims any UP earned from providing liquidity if any exists, and sends the UP to the address provided.

swap

function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;

The swap function exchanges one token for another. Under the hood, all trades on uTrade V2 use this function. The calldata must be 0 during a normal swap, but must contain data if executing a flash loan. Emits the Swap and Sync events.

skim

function skim(address to) external;

The skim function operates as a safeguard if the amount of tokens causes a data error due to too large of a number in the reserves pools. In this unusual circumstance, this will trigger failures in trades. The skim function can be called to return the overflowed tokens to the caller.

sync

function sync() external;

The sync function operates as a safeguard in certain events where the token balance changes outside of normal trading. An example would be an algorithmic stablecoin re-balancing, therefore lowering or raising the amount of the algorithmic stablecoin in the pool. The sync function may be called to reset the price ratio to the new reserves. Emits the Syncevent.

Interface Code

interface IUnifiPair {
    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
    function price0CumulativeLast() external view returns (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}