Wrapper Pools

Learn how an ERC-4626 wrapper pool works, which hook permissions it enables, and how the wrapper hook contracts are organized.

A wrapper pool is a v4 pool whose two currencies are a vault share token and its underlying, and whose behavior is defined entirely by the hook rather than by a liquidity curve:

No liquidity. beforeAddLiquidity unconditionally reverts with LiquidityNotAllowed. The pool never holds reserves of either token between transactions.
No fee. Initialization requires poolKey.fee == 0 (InvalidPoolFee), and beforeSwap returns a zero fee override.
Fixed token pair. Initialization requires the pool's two currencies to be exactly the wrapper and underlying currencies (InvalidPoolToken).

Because the pool holds no reserves, the hook sources tokens through v4 flash accounting during the swap itself (see Swap Mechanics) rather than from a standing balance.

Hook Permissions

getHookPermissions enables exactly four flags:

Permission	Purpose
`beforeInitialize`	Validate the token pair and enforce a zero fee.
`beforeAddLiquidity`	Block all liquidity provision.
`beforeSwap`	Perform the wrap or unwrap and return the swap delta.
`beforeSwapReturnDelta`	Allow `beforeSwap` to return a `BeforeSwapDelta` and take over accounting.

No after* callbacks are used. The hook's deployed address must encode these flags in its low bits, per standard v4 hook address mining.

Contract Hierarchy

BaseHook, DeltaResolver
  └─ BaseTokenWrapperHook              abstract: pool rules, beforeSwap dispatch, delta settlement
       └─ ERC4626WrapperHook           vault deposit/redeem and preview math
            ├─ ERC4626RoutingHook                    quoting twin (overrides _deposit to a preview)
            │    └─ DeallocatingERC4626RoutingHook   deallocating quoting twin
            └─ DeallocatingERC4626WrapperHook        Spark variant (overrides the unwrap source)

BaseTokenWrapperHook is shared by every wrapper hook, including the WETH and wstETH wrappers. It owns the generic machinery: pool validation, the beforeSwap dispatch between wrap and unwrap, liquidity blocking, and the DeltaResolver-based settlement helpers. ERC4626WrapperHook fills in the vault-specific seams: _deposit, _withdraw (which delegates to the overridable _redeemToUnderlying), the previewMint and previewWithdraw helpers, and the exact-output flag.

Hook Permissions

Contract Hierarchy

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