Batch Swap

BEX allows multi-hop swaps, or “batch swaps”, which can optimize routes across multiple liquidity pools to find the best prices. The BEX Vault contract exposes the batchSwap function to allow multi-hop swaps.

Functions

batchSwap

function batchSwap(SwapKind kind,
          BatchSwapStep[] swaps,
          IAsset[] assets,
          FundManagement funds,
          int256[] limits,
          uint256 deadline) returns (int256[] assetDeltas)

Parameter	Type	Description
kind	SwapKind	The type of swap (GIVEN_IN or GIVEN_OUT)
swaps	BatchSwapStep[]	Array of steps in the batch swap
assets	IAsset[]	Array of tokens used in the batch swap
funds	FundManagement	Specifies token sources and destinations
limits	int256[]	Maximum amounts of each asset to be transferred
deadline	uint256	UNIX timestamp by which the swap must complete

Returns	Type	Description
assetDeltas	int256[]	Net token balances resulting from the swap

queryBatchSwap

function queryBatchSwap(SwapKind kind,
          BatchSwapStep[] swaps,
          IAsset[] assets,
          FundManagement funds)
          returns (int256[] assetDeltas)

Returns	Type	Description
assetDeltas	int256[]	Simulated net token balances resulting from the swap

Use this function off-chain to estimate swap results and calculate appropriate limits.

Structs

BatchSwapStep

struct BatchSwapStep {
    bytes32 poolId;
    uint256 assetInIndex;
    uint256 assetOutIndex;
    uint256 amount;
    bytes userData;
}

Field	Type	Description
poolId	bytes32	The id of the pool to swap with
assetInIndex	uint256	The index of the input token within the `assets` array
assetOutIndex	uint256	The index of the output token within the `assets` array
amount	uint256	The amount to swap, interpretation depends on `kind`
userData	bytes	Additional data required by the pool for the swap

Important: When amount is set to 0 in a multi-hop swap, BEX will use the full output of the previous step as input.

FundManagement

struct FundManagement {
    address sender;
    bool fromInternalBalance;
    address payable recipient;
    bool toInternalBalance;
}

Field	Type	Description
sender	address	The address providing tokens for the swap
fromInternalBalance	bool	Whether to use tokens from internal balance
recipient	address payable	The address receiving tokens after the swap
toInternalBalance	bool	Whether to send tokens to internal balance

The SwapKind parameter in the batchSwap function determines how swap amounts are interpreted:

GIVEN_IN: Specify the exact amount of tokens to swap in. The function calculates and returns the amount of tokens you’ll receive. Example: “Swap exactly 100 USDC for as much ETH as possible.”
GIVEN_OUT: Specify the exact amount of tokens to receive. The function calculates and returns the amount of tokens you need to swap in. Example: “Receive exactly 1 ETH, how much USDC do I need to swap?”

The choice between GIVEN_IN and GIVEN_OUT affects how the amount field in the BatchSwapStep struct is interpreted and how swap calculations are performed.

Examples

The following examples demonstrate different ways to use batch swaps in BEX. These patterns can help you optimize trading strategies and reduce gas costs by combining multiple operations into single transactions.

Multi-hop examples

Multi-hop swaps allow trading between tokens that don’t have direct liquidity pools by routing through intermediate tokens. This can often result in better pricing than direct swaps.

Example 1: GIVEN_IN ( $USDC ->$ HONEY -> $DAI)

In this example, you want to swap 1000

USDC through

HONEY to get $DAI. The swap is executed in two steps:

Step	Amount	Token In	Token Out	Description
0	1000	$USDC	$HONEY	Swap exact 1000 $USDC for$ HONEY
1	0	$HONEY	$DAI	Swap all received $HONEY for$ DAI

By setting the second step’s amount to 0, you ensure all $HONEY received from step 0 is used in step 1.

Example 2: GIVEN_OUT ( $USDC ->$ HONEY -> $DAI)

Here you want exactly 500

DAI, and BEX will calculate backwards how much

USDC you need:

Step	Amount	Token Out	Token In	Description
0	500	$DAI	$HONEY	Request exact 500 $DAI output
1	0	$HONEY	$USDC	Calculate required $USDC input

The swap calculates first how much

HONEY is needed for 500

DAI, then how much

USDC is needed for that amount of

HONEY.

Parallel swap examples

Parallel swaps are batch swaps where multiple unrelated swaps are executed in parallel within a single transaction. This allows for efficient execution of multiple trades by batching them together, reducing overall gas costs compared to executing them separately.

Example 3: Parallel GIVEN_IN swaps

Execute multiple independent swaps in a single transaction:

Step	Amount	Token In	Token Out	Description
0	1000	$USDC	$HONEY	Swap 1000 $USDC for$ HONEY
1	0.5	$WETH	$DAI	Swap 0.5 $WETH for$ DAI
2	0.01	$WBTC	$USDC	Swap 0.01 $WBTC for$ USDC

Each swap is independent and executes in parallel, optimizing gas usage.

Example 4: Combined GIVEN_OUT swaps

This example demonstrates how to combine a multi-hop swap with a single-hop swap in parallel, all using GIVEN_OUT mode. It performs two independent swaps:

A multi-hop swap A->B->C->D to get exactly 100 D
A single swap E->F to get exactly 50 F

Step	Amount	Token Out	Token In	Description
0	100	D	C	First step: Request exactly 100 D
1	0	C	B	Second step: Use all C from previous step
2	0	B	A	Third step: Calculate required A input
3	50	F	E	Independent parallel swap: Get exactly 50 F

In this example:

Steps 0-2 form one multi-hop path (A->B->C->D) where you want exactly 100 D
Step 3 is a completely independent swap (E->F) where you want exactly 50 F
BEX will calculate the required amounts of tokens A and E needed as inputs
The two swaps execute in parallel in a single transaction

This pattern is useful when you need exact output amounts from completely independent swap paths.

Overview

Getting Started

Proof of Liquidity

BEX

Bend

Functions

batchSwap

queryBatchSwap

Structs

BatchSwapStep

FundManagement

Examples

Multi-hop examples

Example 1: GIVEN_IN ( $USDC ->$ HONEY -> $DAI)

Example 2: GIVEN_OUT ( $USDC ->$ HONEY -> $DAI)

Parallel swap examples

Example 3: Parallel GIVEN_IN swaps

Example 4: Combined GIVEN_OUT swaps

​Functions

​batchSwap

​queryBatchSwap

​Structs

​BatchSwapStep

​FundManagement

​Examples

​Multi-hop examples

​Example 1: GIVEN_IN (USDC−>USDC -> USDC−>HONEY -> $DAI)

​Example 2: GIVEN_OUT (USDC−>USDC -> USDC−>HONEY -> $DAI)

​Parallel swap examples

​Example 3: Parallel GIVEN_IN swaps

​Example 4: Combined GIVEN_OUT swaps

Functions

batchSwap

queryBatchSwap

Structs

BatchSwapStep

FundManagement

Examples

Multi-hop examples

Example 1: GIVEN_IN ( $USDC ->$ HONEY -> $DAI)

Example 2: GIVEN_OUT ( $USDC ->$ HONEY -> $DAI)

Parallel swap examples

Example 3: Parallel GIVEN_IN swaps

Example 4: Combined GIVEN_OUT swaps