Pool Exits

::: info Calls to exitPool() are made on the Vault contract! You cannot send this command directly to a pool. :::

API

exitPool(
    bytes32 poolId,
    address sender,
    address recipient,
    ExitPoolRequest request
)
 
struct ExitPoolRequest {
    address[] assets,
    uint256[] minAmountsOut,
    bytes userData,
    bool toInternalBalance
}

Arguments Explained

• poolId - ID of the pool you're interacting with
• sender - Address sending BPT
• recipient - Address receiving tokens (usually the same as sender)
• request - ExitPoolRequest tuple made up of the following:
  • assets - List of your tokens, ordered (see below)
  • minAmountsOut - Minimum token receive amounts (see below)
  • userData - Custom bytes field (see below)
  • toInternalBalance - True if you receiving tokens as internal token balances. False if receiving as ERC20.

Token Ordering

When providing your assets, you must ensure that the tokens are sorted numerically by token address. It's also important to note that the values in minAmountsOut correspond to the same index value in assets, so these arrays must be made in parallel after sorting.

minAmountsOut

In the exitPool call, you have to provide minAmountsOut, the lower limits for the tokens to receive. In short, what are the minimum amounts you would find acceptable, given the amount of BPT you are providing?

A good practice would be to user queryExit in BalancerQueries to find the current amounts of tokens you would get for your BPT, and then account for some possible slippage.

Let's say that you want to allow a 1% slippage. After computing how many tokens you expect for a given amount of BPT, you'd apply a factor of 0.99 to all the amounts. These thresholds are important because it's possible for token amounts to change in the pool between the time you send your transaction and the when your transaction executes.

userData

userData is a highly versatile field; as such, it needs to be encoded for its specific use case. For exits, userData encodes a ExitKind to tell the pool what style of exit you're performing. Since pool types are customizable, not every pool necessarily uses the same ExitKind, so it's important to keep track of what each pool type can handle.

WeightedPool ExitKinds

enum ExitKind {
    EXACT_BPT_IN_FOR_ONE_TOKEN_OUT,
    EXACT_BPT_IN_FOR_TOKENS_OUT,
    BPT_IN_FOR_EXACT_TOKENS_OUT,
    MANAGEMENT_FEE_TOKENS_OUT // for InvestmentPool
}

The first three types ofExitKind apply to the following pools:

• WeightedPool
• WeightedPool2Tokens
• LiquidityBootstrappingPool
• InvestmentPool

As noted in the comment, only the InvestmentPool has a fourth:MANAGEMENT_FEE_TOKENS_OUT. This is used as an internal function only, so it is out of the scope of this page.

StablePool ExitKinds

enum ExitKind {
    EXACT_BPT_IN_FOR_ONE_TOKEN_OUT,
    EXACT_BPT_IN_FOR_TOKENS_OUT,
    BPT_IN_FOR_EXACT_TOKENS_OUT
}

Applies to:

• StablePool
• MetaStablePool

Exit Types Explained

• Single Asset Exit (EXACT_BPT_IN_FOR_ONE_TOKEN_OUT)
  • User sends a precise quantity of BPT, and receives an estimated but unknown (computed at run time) quantity of a single token.
• Proportional Exit (EXACT_BPT_IN_FOR_TOKENS_OUT)
  • User sends a precise quantity of BPT, and receives an estimated but unknown (computed at run time) quantities of all tokens.
• Custom Exit (BPT_IN_FOR_EXACT_TOKENS_OUT)
  • User sends an estimated but unknown (computed at run time) quantity of BPT, and receives precise quantities of specified tokens.

Encoding

• Single Asset Exit
  • userData ABI
    • ['uint256', 'uint256', 'uint256']
  • userData
    • [EXACT_BPT_IN_FOR_ONE_TOKEN_OUT, bptAmountIn, exitTokenIndex]
• Proportional Exit
  • userData ABI
    • ['uint256', 'uint256']
  • userData
    • [EXACT_BPT_IN_FOR_TOKENS_OUT, bptAmountIn]
• Custom Exit
  • userData ABI
    • ['uint256', 'uint256[]', 'uint256']
  • userData
    • [BPT_IN_FOR_EXACT_TOKENS_OUT, amountsOut, maxBPTAmountIn]