Introduction to Smart Contracts

What Is a Smart Contract?

A smart contract is a self-executing program that operates on the Ethereum blockchain. It consists of code (functions) and data (state) stored at a specific address on the blockchain. Unlike traditional accounts, smart contracts are not controlled by users but are deployed and executed autonomously.

Key features:

• Immutable: Once deployed, smart contracts cannot be deleted.
• Transparent: Interactions are irreversible and publicly verifiable.
• Self-enforcing: Rules are automatically executed without intermediaries.

Smart contracts function like Ethereum accounts, holding balances and processing transactions when triggered by user interactions.

Prerequisites

Before diving into smart contracts, familiarize yourself with:

1. Ethereum Accounts
2. Transactions
3. Ethereum Virtual Machine (EVM)

For a beginner-friendly overview, explore our Smart Contracts Introduction.

The Digital Vending Machine Analogy

Imagine a smart contract as a vending machine:

• Input: Money + selection.
• Output: Dispensed item.

Example Solidity code for a vending machine contract:

pragma solidity 0.8.7;

contract VendingMachine {
    address public owner;
    mapping(address => uint) public cupcakeBalances;

    constructor() {
        owner = msg.sender;
        cupcakeBalances[address(this)] = 100;
    }

    function refill(uint amount) public {
        require(msg.sender == owner, "Only the owner can refill.");
        cupcakeBalances[address(this)] += amount;
    }

    function purchase(uint amount) public payable {
        require(msg.value >= amount * 1 ether, "Pay at least 1 ETH per cupcake");
        require(cupcakeBalances[address(this)] >= amount, "Not enough cupcakes");
        cupcakeBalances[address(this)] -= amount;
        cupcakeBalances[msg.sender] += amount;
    }
}

👉 Explore more smart contract examples

Permissionless and Composability

Permissionless Deployment

Anyone can write and deploy a smart contract by:

1. Learning a smart contract language (e.g., Solidity).
2. Paying ETH for gas fees (higher for contract deployment).

Composability

Smart contracts are public APIs, enabling:

• Cross-contract calls.
• Dynamic functionality extension.
• Learn more about composability.

Limitations

1. No Off-Chain Data: Smart contracts can’t fetch real-world data directly. Solutions like oracles bridge this gap.
2. Size Constraints: Max 24 KB per contract. Workarounds include the Diamond Pattern.

Multisignature (Multisig) Contracts

Multisig contracts require multiple signatures (e.g., 3/5 or 4/7) to execute transactions, enhancing security for:

• DAO governance.
• High-value fund management.

Example: A 4/7 multisig ensures funds are recoverable even if 3 keys are lost.

Smart Contract Resources

• OpenZeppelin Contracts: Secure library for development (GitHub).
• Coinbase Guide: What Is a Smart Contract?
• Video Explanation: Smart Contracts Simplified

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FAQ

Q: Can smart contracts be modified after deployment?
A: No, they’re immutable by design.

Q: How do smart contracts interact with external data?
A: Via oracles (e.g., Chainlink).

Q: What’s the cost of deploying a smart contract?
A: Depends on gas fees and contract complexity.

Ready to build? Start with Solidity documentation.