@balancer-labs/v2-pool-weighted

Balancer V2 Weighted Pools

This package contains the source code for Balancer V2 Weighted Pools, that is, Pools that swap tokens by enforcing a Constant Weighted Product invariant.

The two basic flavors currently in existence are WeightedPool (basic twenty token version) and WeightedPool2Tokens (limited to two tokens, but supporting price oracles).

The smart directory contains a number of 'smart' variants, which automatically update some of their attributes to support more complex use cases. Examples are LiquidityBootstrappingPool for auction-like mechanisms, and InvestmentPool for managed portfolios.

⚠️	Investment Pools are still undergoing development and may contain bugs and/or change significantly.

Other useful contracts include WeightedMath, which implements the low level calculations required for swaps, joins, exits and price calculations, and IPriceOracle, used to make price oracle queries.

Overview

Installation

$ npm install @balancer-labs/v2-pool-weighted

Usage

This package can be used in multiple ways, including interacting with already deployed Pools, performing local testing, or even creating new Pool types that also use the Constant Weighted Product invariant.

To get the address of deployed contracts in both mainnet and various test networks, see v2-deployments.

Sample contract that performs an action conditionally using a Pool as a price oracle:

pragma solidity ^0.7.0;

import "@balancer-labs/v2-pool-weighted/contracts/IPriceOracle.sol";

contract SimpleOracleQuery {
    IPriceOracle private constant oracle = "0x0b09deA16768f0799065C475bE02919503cB2a35"; // WETH-DAI Pool

    function performAction() external {
      IPriceOracle.OracleAverageQuery[] memory queries = new IPriceOracle.OracleAverageQuery[](1);

      // Average price over the last hour - note that the oracle must be fully initialized
      queries[0] = IPriceOracle.OracleAverageQuery({
        variable: IPriceOracle.Variable.PAIR_PRICE,
        secs: 3600,
        ago: 0
      });

      uint256[] memory results = oracle.getTimeWeightedAverage(queries);
      if (results[0] >= 4000) {
        ...
      } else {
        ...
      }
    }
}

Sample Weighted Pool that computes weights dynamically on every swap, join and exit:

pragma solidity ^0.7.0;

import '@balancer-labs/v2-pool-weighted/contracts/BaseWeightedPool.sol';

contract DynamicWeightedPool is BaseWeightedPool {
    uint256 private immutable _creationTime;

    constructor() {
        _creationTime = block.timestamp;
    }

    function _getNormalizedWeightsAndMaxWeightIndex() internal view override returns (uint256[] memory) {
        uint256[] memory weights = new uint256[](2);

        // Change weights from 50-50 to 30-70 one month after deployment
        if (block.timestamp < (_creationTime + 1 month)) {
          weights[0] = 0.5e18;
          weights[1] = 0.5e18;
        } else {
          weights[0] = 0.3e18;
          weights[1] = 0.7e18;
        }

        return (weights, 1);
    }

    ...
}

Licensing

GNU General Public License Version 3 (GPL v3).