Why Use a fallback or receive Function?

Direct Ether Transfers:

• If someone sends Ether directly to the contract address (without calling deposit()), the transaction would fail unless a receive or fallback function is present.
• For example, transfers using:

contractAddress.send(1 ether);
contractAddress.transfer(1 ether);        

Users might not always call the deposit() function intentionally and might simply send Ether directly to the contract.

A receive function ensures the contract handles these situations gracefully.

A receive() function is slightly cheaper than calling a deposit() function because it doesn't involve function selector calculations.

--> AND VERY IMPORTANT:

External tools, services, or contracts interacting with your smart contract may send Ether directly. A receive function ensures compatibility with such interactions.

If no receive or fallback function is implemented, any direct Ether transfer will cause the transaction to revert. This might confuse users or result in failed interactions.

When You Don't Need a receive Function

• You can skip implementing a receive or fallback function if:

Your contract is designed to accept Ether exclusively through deposit() and you enforce this rigorously.

Example:

function deposit() external payable {
    require(msg.value > 0, "Must send Ether to deposit");
    balances[msg.sender] += msg.value;
}        

Receive vs. Fallback

• receive(): Executes when the contract receives Ether without any data (plain Ether transfer).

receive() external payable {
    balances[msg.sender] += msg.value;
}        

• fallback(): Executes when Eth is sent with data that doesn't match any function. The contract is called without a matching function signature.

fallback() external payable {
    // Optional: You can handle Ether or log an event here.
}        

Which to Use?

• If you only expect Ether transfers, use receive().
• If you want to handle both Ether transfers and unexpected calls, use fallback().

Final Takeaway

You don’t need a fallback or receive function if you only want to accept Ether explicitly via deposit().

However, having one provides better user experience, broader compatibility, and robustness in case of unexpected interactions.

Would you like to see an example without the receive function? comment "EXAMPLE" below !