Sending and Receiving Ether

Solidity provides multiple ways to send and receive Ether between contracts and accounts. Understanding these methods is essential for writing secure contracts.

1) Payable functions

• Functions marked with payable can receive Ether.
• Non-payable functions reject any Ether sent, otherwise the transaction reverts.

Example:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract PayableExample {
    uint256 public balance;

    // Function can receive Ether
    function deposit() public payable {
        balance += msg.value;
    }

    // Function cannot receive Ether
    function notPayable() public {
        // Any Ether sent here will revert
    }
}

• msg.value contains the amount of Ether sent.
• msg.sender is the address sending the Ether.

2) Sending Ether

Solidity provides three primary methods: transfer, send, and call.

a) transfer

• Sends Ether and reverts on failure.
• Forward gas limit: 2300 gas.

payable(recipient).transfer(1 ether);

b) send

• Sends Ether and returns a boolean indicating success.
• Forward gas limit: 2300 gas.
• Manual error handling is required.

bool success = payable(recipient).send(1 ether);
require(success, "Send failed");

c) call

• Low-level function, recommended in Solidity >= 0.6 for sending Ether.
• Forwards all remaining gas unless specified.
• Returns a boolean and data.

(bool success, ) = payable(recipient).call{value: 1 ether}("");
require(success, "Call failed");

Key points:

• transfer and send are limited to 2300 gas, enough for a fallback function.
• call is flexible and safer for interacting with contracts that require more gas.

3) Receiving Ether

Contracts can receive Ether via receive or fallback functions:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract ReceiveEther {
    event Received(address sender, uint256 amount);

    // Triggered when contract receives Ether with empty calldata
    receive() external payable {
        emit Received(msg.sender, msg.value);
    }

    // Triggered for non-existent function calls or data sent
    fallback() external payable {
        emit Received(msg.sender, msg.value);
    }
}