uniswap-v4-expert

Uniswap V4 Expert

Architecture Overview

Uniswap V4 replaces V3's factory-per-pool model with a singleton PoolManager — every pool lives inside a single contract. This eliminates redundant bytecode deployments and enables multi-hop swaps to settle only net token transfers. All state-changing operations use flash accounting via EIP-1153 transient storage: callers accumulate deltas during an unlock() callback and must zero out all balances before the callback returns.

Singleton Design

┌────────────────────────────────────────────┐
│                 PoolManager                │
│  ┌──────────┐ ┌───────────┐ ┌──────────┐   │
│  │  Pool A  │ │  Pool B   │ │  Pool C  │   │
│  │ ETH/USDC │ │ WBTC/USDC │ │ ETH/DAI  │   │
│  └──────────┘ └───────────┘ └──────────┘   │
│                                            │
│  Transient Storage (EIP-1153)              │
│  ┌──────────────────────────────────────┐  │
│  │ currency → delta mapping (per lock)  │  │
│  └──────────────────────────────────────┘  │
└────────────────────────────────────────────┘

Flash Accounting Flow

1. Caller invokes poolManager.unlock(data)
2. PoolManager calls IUnlockCallback(msg.sender).unlockCallback(data)
3. Inside the callback, caller executes operations (swap, modifyLiquidity, donate)
4. Each operation updates transient storage deltas — no token transfers yet
5. Caller resolves deltas via settle() (pay tokens in) and take() (withdraw tokens out)
6. On return from unlockCallback, PoolManager verifies all currency deltas are zero
7. If any delta is nonzero, the transaction reverts with CurrencyNotSettled()

This means multi-hop swaps (e.g., A→B→C) only require net token movements for A and C, saving gas on intermediate transfers.

Functions Callable Outside unlock()

Functions callable outside unlock():

• initialize() — creates a new pool (no balance changes)
• sync(currency) — snapshots reserves into transient storage; harmless outside a lock
• updateDynamicLPFee() — called by hook contracts to set the current dynamic fee
• the IProtocolFees admin functions (setProtocolFeeController, setProtocolFee, collectProtocolFees)