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# Pair

This documentation covers Xchange-specific functionality. For ERC-20 functionality, see Pair (ERC-20).

# Code

XchangePair.sol

# Address

See Pair Addresses.

# Events

# Mint

event Mint(address indexed sender, uint amount0, uint amount1); Emitted each time liquidity tokens are created via mint.

# Burn

event Burn(address indexed sender, uint amount0, uint amount1, address indexed to); Emitted each time liquidity tokens are destroyed via burn.

# Swap 

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

Emitted each time a swap occurs via swap.

# Sync 

event Sync(uint112 reserve0, uint112 reserve1);

Emitted each time reserves are updated via mint, burn, swap, or sync.

# Read-Only Functions

# MINIMUM_LIQUIDITY 

function MINIMUM_LIQUIDITY() external pure returns (uint);

Returns 1000 for all pairs. See Minimum Liquidity.

# factory 

function factory() external view returns (address);

Returns the factory address.

# token0 

function token0() external view returns (address);

Returns the address of the pair token with the lower sort order.

# token1 

function token1() external view returns (address);

Returns the address of the pair token with the higher sort order.

# getReserves 

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

Returns the reserves of token0 and token1 used to price trades and distribute liquidity. See Pricing. Also returns the block.timestamp (mod 2**32) of the last block during which an interaction occured for the pair.

# price0CumulativeLast 

function price0CumulativeLast() external view returns (uint);

See Oracles.

# price1CumulativeLast 

function price1CumulativeLast() external view returns (uint);

See Oracles.

# kLast

function kLast() external view returns (uint); Returns the product of the reserves as of the most recent liquidity event. See Protocol Charge Calculation.

# State-Changing Functions

# Xchange features

# initialize 

  function initialize(address, address) external;

# mustBurn 

  function mustBurn(address to, uint256 gasAmount) external returns (uint256 amount0, uint256 amount1);

mustBurn is similar to burn, functions present in the UniswapV2 protocol. However, they contain various countermeasures to ensure these calls always succeed. These countermeasures include configurable gas limits and best effort calls. They prevent ecosystem owned liquidity from being trapped within the pair contract due to accidental or intentional pathological token contracts.

# swapWithDiscount 

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

swapWithDiscount is a modified version of swap which allows a caller to assert they should be granted a discount.

If the caller is an untrusted party, the msg.sender is validated against the Discount Authority contract. This check is skipped if the caller is a trusted authority. This enables the use of a peripheral router contract.

This functionality exists to ensure that the swap gas cost is not affected by the discount capability except when a caller chooses to request that they be discounted. This ensures the default gas cost of interacting with the pair is similar to the existing implementations of the UniswapV2 protocol.

# syncSafe 

  function syncSafe(uint256 gasAmountToken0, uint256 gasAmountToken1) external;

syncSafe is similar to sync, functions present in the UniswapV2 protocol. However, they contain various countermeasures to ensure these calls always succeed. These countermeasures include configurable gas limits and best effort calls. They prevent ecosystem owned liquidity from being trapped within the pair contract due to accidental or intentional pathological token contracts.

# withdrawTokensAgainstMinimumBalance 

  function withdrawTokensAgainstMinimumBalance(address tokenAddress, address to, uint112 amount) external returns (uint112);

Used by trusted external addresses to remove tokens while simultaneously reducing the set minimum balance. This is the functionality that allows loan liquidation while also protecting the token balance greater than the loan amount from being withdrawn.

# setMinimumBalance 

  function setMinimumBalance(address tokenAddress, uint112 minimumAmount) external;

Callable only by a trusted address to prevent the associated balance of tokens drop below that amount. All external calls are checked against these minimum values.

# mint 

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

Creates pool tokens.

  • Emits Mint, Sync, Transfer.

# burn 

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

Destroys pool tokens.

  • Emits Burn, Sync, Transfer.

# swap 

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

Swaps tokens. For regular swaps, data.length must be 0. Also see Flash Swaps.

  • Emits Swap, Sync.

# skim 

function skim(address to) external;

See the whitepaper.

# sync 

function sync() external;

See the whitepaper.

  • Emits Sync.

# Interface 

pragma solidity >=0.5.0;

interface IXchangeV2Pair {
  event Approval(address indexed owner, address indexed spender, uint value);
  event Transfer(address indexed from, address indexed to, uint value);

  function name() external pure returns (string memory);
  function symbol() external pure returns (string memory);
  function decimals() external pure returns (uint8);
  function totalSupply() external view returns (uint);
  function balanceOf(address owner) external view returns (uint);
  function allowance(address owner, address spender) external view returns (uint);

  function approve(address spender, uint value) external returns (bool);
  function transfer(address to, uint value) external returns (bool);
  function transferFrom(address from, address to, uint value) external returns (bool);

  function DOMAIN_SEPARATOR() external view returns (bytes32);
  function PERMIT_TYPEHASH() external pure returns (bytes32);
  function nonces(address owner) external view returns (uint);

  function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;

  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;

  // Xchange additional features
  function initialize(address, address) external;

  function mustBurn(address to, uint256 gasAmount) external returns (uint256 amount0, uint256 amount1);
  function swapWithDiscount(uint amount0Out, uint amount1Out, address to, uint feeAmountOverride, bytes calldata data) external;
  function syncSafe(uint256 gasAmountToken0, uint256 gasAmountToken1) external;

  function withdrawTokensAgainstMinimumBalance(address tokenAddress, address to, uint112 amount) external returns (uint112);
  function setMinimumBalance(address tokenAddress, uint112 minimumAmount) external;

}

ABI

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