L1-5: Token Wrapper (WETH) #

1. Problem #

Create an ERC20-compatible wrapper token for ETH. Users deposit ETH to receive WETH, and burn WETH to withdraw ETH, at a 1:1 exchange rate.

2. Why #

Native ETH does not conform to the ERC20 standard and cannot directly interact with DeFi protocols. WETH serves as an ERC20 equivalent of ETH:

• All DeFi protocols use the same interface to handle tokens
• ETH holders can participate in AMMs, lending, and other protocols
• Protocols do not need special handling for native ETH

3. Solution #

Inherit OpenZeppelin ERC20 #

contract WrappedETH is ERC20("WrappedEth", "WETH")

Core Functions #

• deposit() payable: ETH → WETH (mint)
• withdraw(uint256): WETH → ETH (burn + transfer)
• receive(): auto deposit

4. Pitfalls Encountered #

4.1 Direct ETH transfers are ignored #

Without implementing receive(), users sending ETH directly to the contract will be rejected or silently lost.

4.2 Function name conflicts with event name #

The deposit function name and Deposit event name can cause ambiguity in Solidity. When calling deposit() inside receive(), the compiler may raise an error.

4.3 Insufficient balance not checked #

Not checking the balance in withdraw will cause the burn to fail.

5. Why the Pitfalls Happen #

5.1 #

Contracts without receive() revert when receiving ETH. Users who forget to call deposit() and send ETH directly will have their transaction fail.

5.2 #

When calling deposit() inside the receive function, the Solidity compiler may resolve deposit as a reference to the Deposit event rather than the function. Use this.deposit() or inline the logic.

5.3 #

OZ ERC20's _burn checks the balance, but not checking at the withdraw entry first could waste gas on a failed burn.

6. How to Resolve the Pitfalls #

• Implement receive() external payable with inlined deposit logic
• In withdraw, check require(balanceOf(msg.sender) >= amount) first
• Use explicit this.deposit() or write the logic directly in receive

7. Technical Highlights #