# Pair Addresses

## 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](https://github.com/Uniswap/uniswap-v2-core/blob/master/contracts/UniswapV2Factory.sol#L32), we can also compute pair addresses *without any on-chain lookups* because of [CREATE2](https://eips.ethereum.org/EIPS/eip-1014). The following values are required for this technique:

|                        |                                                                      |
| ---------------------- | -------------------------------------------------------------------- |
| `address`              | The factory address                                                  |
| `salt`                 | `keccak256(abi.encodePacked(token0, token1))`                        |
| `keccak256(init_code)` | `0x96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f` |

* `token0` must be strictly less than `token1` by sort order.
* Can be computed offline.
* Requires the ability to perform `keccak256`.

### Examples

#### 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.

```typescript
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
)
```