# Flashloan (V3)

Pulsar pools provide `flash` method to flashloan.

### Flow

<figure><img src="/files/VelwDGrpIiHZuk8sdzYs" alt=""><figcaption></figcaption></figure>

### Implementation for Flashing Contract (Solidity)

```solidity
import '@cryptoalgebra/core/contracts/interfaces/IAlgebraPool.sol';
import '@cryptoalgebra/core/contracts/interfaces/callback/IAlgebraFlashCallback.sol';

import '@cryptoalgebra/periphery/contracts/libraries/TransferHelper.sol';

contract SimpleFlasher {
	// Variables so we can verify callback
	address poolCalled;
	uint256 amount0;
	uint256 amount1;
	
	function flash(
	    address pool,
	    address recipient,
	    uint256 _amount0,
	    uint256 _amount1
	  ) external {
			// setting the variables
			poolCalled = pool;
			amount0 = _amount0;
			amount1 = _amount1;
	
			// requesting flash loan to `recipient` address
	    IAlgebraPool(pool).flash(recipient, amount0, amount1, bytes(''));
			
			// cleaning up
			poolCalled = address(0);
			amount0 = 0;
			amount1 = 0;
	  }
	
	  function algebraFlashCallback(
	    uint256 fee0,
	    uint256 fee1,
	    bytes calldata data
	  ) external override {
			require(msg.sender == poolCalled, "only pool can call");
	
			// do the magic here ...
	
			// repay to pool
			TransferHelper.safeTransfer(IAlgebraPool(msg.sender).token0(), msg.sender, amount0 + fee0);
			TransferHelper.safeTransfer(IAlgebraPool(msg.sender).token1(), msg.sender, amount1 + fee1);
	  }
}
```

### More Optimal Implementation for Flashing Contract (Javascript)

```javascript
import '@cryptoalgebra/core/contracts/interfaces/IAlgebraPool.sol';
import '@cryptoalgebra/core/contracts/interfaces/callback/IAlgebraFlashCallback.sol';

import '@cryptoalgebra/periphery/contracts/libraries/CallbackValidation.sol';
import '@cryptoalgebra/periphery/contracts/libraries/TransferHelper.sol';

contract MoreOptimalFlasher {
  address immutable poolDeployer; // address of AlgebraPoolDeployer contract

	constructor(_poolDeployer) {
		poolDeployer = _poolDeployer;
	}

	function flash(
	    address pool,
	    address recipient,
	    uint256 amount0,
	    uint256 amount1
	  ) external {
			address token0 = IAlgebraPool(pool).token0();
			address token1 = IAlgebraPool(pool).token1();
			
			// requesting flash loan to `recipient` address
	    IAlgebraPool(pool).flash(recipient, amount0, amount1, abi.encode(token0, token1, amount0, amount1));
	  }
	
	  function algebraFlashCallback(
	    uint256 fee0,
	    uint256 fee1,
	    bytes calldata data
	  ) external override {
			(address token0, address token1, uint256 amount0, uint256 amount1) = abi.decode(data, (address, adrress, uint256, uint256));
			CallbackValidation.verifyCallback(poolDeployer, token0, token1) // check if method is called by algebra pool, revert otherwise
	
			// do the magic here ...
	
			// repay to pool
			TransferHelper.safeTransfer(token0, msg.sender, amount0 + fee0);
			TransferHelper.safeTransfer(token1, msg.sender, amount1 + fee1);
	  }
}
```


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