> ## Documentation Index
> Fetch the complete documentation index at: https://tech.ramses.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Calling Flash

## Parameter Structs

`FlashParams` contains the token addresses, amounts to borrow, and three fee tiers (source pool + two arb pools):

```solidity theme={null}
  struct FlashParams {
        address token0;
        address token1;
        uint24 fee1;
        uint256 amount0;
        uint256 amount1;
        uint24 fee2;
        uint24 fee3;
    }
```

`FlashCallbackData` is passed through to the callback. `poolKey` (from the `PoolAddress` library) identifies the source pool:

```solidity theme={null}
    struct FlashCallbackData {
        uint256 amount0;
        uint256 amount1;
        address payer;
        PoolAddress.PoolKey poolKey;
        uint24 poolFee2;
        uint24 poolFee3;
    }
```

## Calling Flash

Compute the pool address from the pool key, then call `flash` with the callback data abi-encoded:

```solidity theme={null}
    function initFlash(FlashParams memory params) external {
        PoolAddress.PoolKey memory poolKey =
            PoolAddress.PoolKey({token0: params.token0, token1: params.token1, fee: params.fee1});
        IUniswapV3Pool pool = IUniswapV3Pool(PoolAddress.computeAddress(factory, poolKey));
        pool.flash(
            address(this),
            params.amount0,
            params.amount1,
            abi.encode(
                FlashCallbackData({
                    amount0: params.amount0,
                    amount1: params.amount1,
                    payer: msg.sender,
                    poolKey: poolKey,
                    poolFee2: params.fee2,
                    poolFee3: params.fee3
                })
            )
        );
    }
```