# Pair Addresses

## getPair <a href="#getpair" id="getpair"></a>

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 <a href="#create2" id="create2"></a>

Thanks to some [fancy footwork in the factory](https://docs.ws.exchange/reference/smart-contracts), 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](https://docs.ws.exchange/reference/smart-contracts) |
| `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 <a href="#examples" id="examples"></a>

#### TypeScript <a href="#typescript" id="typescript"></a>

This example makes use of the [WhiteSwap SDK](https://docs.ws.exchange/reference/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 '@whiteswap/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'
)
```