ERC-20 Token Standard

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概要

ERC-20 is the Ethereum standard for fungible tokens (identical, interchangeable). Think of them like dollars, one unit equals another. ERC-20 contracts define balances, transfers, and approvals. Every major token (USDC, DAI, LINK) is ERC-20. Learning takes 1-2 weeks for Solidity devs; mastery (minting, burning, access control, security) takes 2-3 months. Senior token engineers earn $150K+ because poorly-designed tokens leak millions to hacks.

ERC-20 Token Standardとは

ERC-20 is Ethereum's standard for fungible tokens, digital assets where each unit is identical and interchangeable. Think of them like dollars: one $1 bill equals another $1 bill. ERC-20 contracts implement a standard interface: balanceOf (check balance), transfer (send tokens), approve (allow someone else to spend), and transferFrom (spend approved tokens). Exchanges, wallets, and DeFi protocols understand ERC-20 because the interface is standardized. Deploy an ERC-20 contract and it automatically works on OpenSea, Uniswap, MetaMask, no integration needed.

🔧 ツール＆エコシステム

SolidityOpenZeppelin contractsHardhat or TruffleWeb3.js or Ethers.jsMetaMaskRemix IDE

💰 地域別給与

地域	ジュニア	ミドル	シニア
USA	$90k	$150k	$230k
UK	$55k	$92k	$140k
EU	$60k	$100k	$150k
CANADA	$95k	$160k	$250k

🎓 認定資格

ERC-20 Specification OpenZeppelin ERC-20 Implementation Solidity by Example, ERC-20

❓ よくある質問

What's the difference between transfer() and transferFrom()?

transfer: I send tokens directly from my wallet to someone else. transferFrom: Someone already approved me to spend X tokens, and I move them. Approve first, then transferFrom. Like pre-authorizing a merchant to charge your card.

Why do I need approve() before transferFrom()?

Security. If transfer was automatic, approving a contract to swap tokens would give it unlimited access to your wallet. Approve limits the contract's spending to a specific amount. Revoke approval when done.

What happens if total supply is unlimited?

Token value approaches zero due to inflation. Most tokens cap total supply. Some (like Ethereum's ETH) don't have a hard cap, but have emission schedules. Set totalSupply to a number and enforce it.

How do I implement taxes or fees on transfers?

Override transfer() and transferFrom(). Calculate 2% fee, send to treasury, transfer remaining 98% to recipient. But this breaks expected behavior, users send 100 tokens, receive 98. Consider this UX impact.

Can I make tokens non-transferable?

Yes. Override transfer and revert if !isOwner. Used for vesting tokens (employees can't sell for X years). Or use pausable pattern: owner can pause transfers globally.

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