Ethereum Denominations and Address Types

This example demonstrates Ethereum's various denominations (wei, gwei, ether) and the differences between address types.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract EthereumDenominations {
    // Ethereum denominations
    uint public constant WEI_IN_GWEI = 1e9;      // 1 gwei = 10^9 wei
    uint public constant WEI_IN_ETHER = 1e18;    // 1 ether = 10^18 wei

    // Address types
    address public immutable owner;               // Regular address (cannot receive ether)
    address payable public treasury;              // Payable address (can receive ether)

    // Track balances
    mapping(address => uint256) public balances;

    constructor() {
        owner = msg.sender;
        treasury = payable(msg.sender);  // Convert regular address to payable
    }

    // Demonstrate wei conversions
    function convertWeiToGwei(uint256 _wei) public pure returns (uint256) {
        return _wei / WEI_IN_GWEI;  // Convert wei to gwei
    }

    function convertWeiToEther(uint256 _wei) public pure returns (uint256) {
        return _wei / WEI_IN_ETHER; // Convert wei to ether
    }

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

    function withdrawToTreasury() public {
        require(msg.sender == owner, "Only owner can withdraw");
        uint256 balance = address(this).balance;

        // Transfer to payable address
        (bool success, ) = treasury.call{value: balance}("");
        require(success, "Transfer failed");
    }

    // Demonstrate address conversion
    function updateTreasury(address _newTreasury) public {
        require(msg.sender == owner, "Only owner can update treasury");
        treasury = payable(_newTreasury);  // Convert regular address to payable
    }

    // Get contract balance
    function getBalance() public view returns (uint256) {
        return address(this).balance;
    }
}

Key Concepts

1. Ethereum Denominations

   • 1 ether = 10^9 gwei = 10^18 wei
   • Wei is the smallest denomination
   • All internal calculations use wei
   • Gas prices typically quoted in gwei

2. Address Types

   • address: Cannot receive ether
   • address payable: Can receive ether
   • Regular addresses can be converted to payable using payable()

3. Common Denominations Table

Unit	Wei Value	Wei	Common Usage
wei	1	1	Raw calculations
kwei	1e3	1,000	Rarely used
mwei	1e6	1,000,000	Rarely used
gwei	1e9	1,000,000,000	Gas prices
szabo	1e12	1,000,000,000,000	Legacy unit
finney	1e15	1,000,000,000,000,000	Legacy unit
ether	1e18	1,000,000,000,000,000,000	Main unit

Best Practices

1. Always use wei for internal calculations
2. Convert human-readable ether values to wei when accepting input
3. Use address payable only when ether transfers are needed
4. Always check return value of ether transfers
5. Include fallback functions (receive()) to accept ether