getPair

The most obvious way to get the address for a pair is to call getPair on the factory. If the pair exists, this function will return its address, else address(0) (0x0000000000000000000000000000000000000000).

• The “canonical” way to determine whether or not a pair exists.
• Requires an on-chain lookup.

CREATE2

Thanks to some fancy footwork in the factory, we can also compute pair addresses without any on-chain lookups because of CREATE2. The following values are required for this technique:

• token0 must be strictly less than token1 by sort order.

• Can be computed offline.
• Requires the ability to perform keccak256.

Examples

Solidity

address factory = 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f;
address token0 = 0xCAFE000000000000000000000000000000000000; // change me!
address token1 = 0xF00D000000000000000000000000000000000000; // change me!

address pair = address(uint(keccak256(abi.encodePacked(
  hex'ff',
  factory,
  keccak256(abi.encodePacked(token0, token1)),
  hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f'
))));
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Typescript

This example makes use of the Uniswap SDK. In reality, the SDK computes pair addresses behind the scenes, obviating the need to compute them manually like this.

import { FACTORY_ADDRESS, INIT_CODE_HASH } from '@uniswap/sdk'
import { pack, keccak256 } from '@ethersproject/solidity'
import { getCreate2Address } from '@ethersproject/address'

const token0 = '0xCAFE000000000000000000000000000000000000' // change me!
const token1 = '0xF00D000000000000000000000000000000000000' // change me!

const pair = getCreate2Address(
  FACTORY_ADDRESS,
  keccak256(['bytes'], [pack(['address', 'address'], [token0, token1])]),
  INIT_CODE_HASH'
)
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