Blockchain Smart Contracts with Solidity · レッスン

ERC-20代替可能トークン標準

交換可能なトークンを作成するためのERC-20標準の仕様と機能を理解します。

「ERC-20代替可能トークン標準」はCoddyKit上の無料Blockchain Smart Contracts with Solidityレッスンです。これはレッスン1/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはBlockchain Smart Contracts with Solidity学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Blockchain Smart Contracts with Solidityコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Intro to Blockchain Tokens

Welcome to the world of blockchain tokens! Beyond cryptocurrencies like Ether, blockchains host many other digital assets.

These assets, often called 'tokens', can represent anything from digital currency to ownership of real-world items, or even voting rights in a decentralized organization.

Fungibility: Interchangeable Assets

A key concept for tokens is fungibility. What does it mean?

Fungible: Each unit is identical and interchangeable with another. Like a dollar bill – one $1 bill is the same as any other $1 bill.
Non-Fungible: Each unit is unique and cannot be replaced by another. Like a piece of art or a specific house.

ERC-20 tokens are fungible, meaning every token is equal to every other token of the same type.

Meet the ERC-20 Standard

ERC-20 (Ethereum Request for Comment 20) is a technical standard for fungible tokens on the Ethereum blockchain.

It defines a common set of rules that all compliant tokens must follow. This ensures they can interact seamlessly with wallets, exchanges, and other smart contracts.

Interoperability Through Standards

Why is a standard so important?

Compatibility: Any wallet that supports ERC-20 can manage any ERC-20 token.
Ecosystem Growth: Decentralized applications (dApps) can easily integrate different tokens.
Predictable Behavior: Developers know exactly how an ERC-20 token will behave, making integration safer and faster.

Core Function: `totalSupply()`

The totalSupply() function returns the total number of tokens in existence. It's a public view function, meaning it doesn't change the blockchain state and costs no gas to call.

Try running this simple contract to see how totalSupply might be represented:

pragma solidity ^0.8.0;

contract SimpleTokenInfo {
    uint256 public totalTokens = 1000; // Example supply

    function totalSupply() public view returns (uint256) {
        return totalTokens;
    }
}

Core Function: `balanceOf()`

The balanceOf(address account) function returns the token balance of a specific address. It helps you check how many tokens a user owns.

Let's add balanceOf to our example. The deployer will start with all tokens.

pragma solidity ^0.8.0;

contract SimpleTokenInfo {
    uint256 public totalTokens = 1000;
    mapping(address => uint256) public balances;

    constructor() {
        balances[msg.sender] = totalTokens; // Assign all to deployer
    }

    function totalSupply() public view returns (uint256) {
        return totalTokens;
    }

    function balanceOf(address account) public view returns (uint256) {
        return balances[account];
    }
}

Core Function: `transfer()`

The transfer(address recipient, uint256 amount) function allows the sender of the transaction to send tokens directly to another address.

This is the most common way to move tokens between users.

pragma solidity ^0.8.0;

contract SimpleTokenInfo {
    uint256 public totalTokens = 1000;
    mapping(address => uint256) public balances;

    constructor() {
        balances[msg.sender] = totalTokens;
    }

    function totalSupply() public view returns (uint256) {
        return totalTokens;
    }

    function balanceOf(address account) public view returns (uint256) {
        return balances[account];
    }

    function transfer(address recipient, uint256 amount) public returns (bool) {
        require(balances[msg.sender] >= amount, "Insufficient balance");
        balances[msg.sender] -= amount;
        balances[recipient] += amount;
        return true;
    }
}

Delegated Transfers: `approve()` & `allowance()`

ERC-20 also supports delegated transfers, where one user (the owner) allows another address (the spender) to move tokens on their behalf.

approve(address spender, uint256 amount): The owner grants permission to a spender to withdraw a specific amount of tokens.
allowance(address owner, address spender): Returns the amount of tokens that the spender is currently allowed to withdraw from the owner.

Executing Delegated Transfers: `transferFrom()`

Once an approve() call has been made, the designated spender can then use the transferFrom() function.

transferFrom(address sender, address recipient, uint256 amount): Allows a spender to transfer amount tokens from the sender's balance to the recipient, provided the spender has enough allowance from the sender.

Tracking Actions: ERC-20 Events

ERC-20 defines two standard events: Transfer and Approval. These events are crucial for off-chain applications (like wallets or block explorers) to track token movements and approvals without having to read the entire blockchain state.

They emit logs that can be efficiently indexed and queried.

pragma solidity ^0.8.0;

contract EventExample {
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function demonstrateTransferEvent(address _to, uint256 _value) public {
        // Imagine actual transfer logic here
        emit Transfer(msg.sender, _to, _value);
    }

    function demonstrateApprovalEvent(address _spender, uint256 _value) public {
        // Imagine actual approval logic here
        emit Approval(msg.sender, _spender, _value);
    }
}

Check Your Understanding

The ERC-20 standard outlines specific functions that all compliant tokens must implement. Understanding these is crucial for working with tokens.

ERC-20: Your Token Blueprint

You've now learned about the ERC-20 Fungible Token Standard! It's the blueprint for most interchangeable tokens on Ethereum.

It defines core functions like totalSupply(), balanceOf(), and transfer().
It enables delegated transfers with approve(), allowance(), and transferFrom().
Standard events Transfer and Approval help track token activity.

This standard ensures that all ERC-20 tokens are compatible, making the Ethereum ecosystem robust and easy to navigate. Next, we'll dive into implementing your own ERC-20 token!

よくある質問

「ERC-20代替可能トークン標準」レッスンは無料ですか？

はい。「ERC-20代替可能トークン標準」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Blockchain Smart Contracts with Solidityコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Blockchain Smart Contracts with Solidityコースには全4レッスンが含まれています。

「ERC-20代替可能トークン標準」で何を学びますか？

交換可能なトークンを作成するためのERC-20標準の仕様と機能を理解します。ブラウザで直接実行するハンズオンコードでBlockchain Smart Contracts with Solidityを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Blockchain Smart Contracts with Solidityを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのBlockchain Smart Contracts with Solidityは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン1/4です。

「ERC-20代替可能トークン標準」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このBlockchain Smart Contracts with Solidityレッスンでコードを書いて実行できますか？

はい。すべてのBlockchain Smart Contracts with Solidityレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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