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easyBlockchain Developer interview question

Compare ERC-20, ERC-721 and ERC-1155. When would you use each?

What the interviewer wants to hear

  • ERC-20 is for fungible tokens where every unit is the same
  • ERC-721 is for unique tokens, each ID has one owner
  • ERC-1155 handles many token types, fungible and non-fungible, in one contract
  • ERC-1155 supports batch transfers and saves gas
  • Safe transfer callbacks in 721 and 1155 need care

Model answer

ERC-20 is the standard for fungible tokens, where every unit is interchangeable, like a stablecoin or governance token. It defines balanceOf, transfer, approve, transferFrom and allowance, plus Transfer and Approval events. ERC-721 is for non-fungible tokens: each token ID is unique and has exactly one owner, which suits art, tickets or property deeds, and it has metadata through tokenURI. ERC-1155 is a multi-token standard where one contract manages many IDs, and each ID can have any supply, so a game can have gold coins and unique swords together. It supports batch transfers and balance queries, which cuts gas a lot. I pick ERC-20 for currencies, ERC-721 when each item is truly unique and needs wide marketplace support, and ERC-1155 for games or editions. With 721 and 1155, I remember that safe transfers call the receiver, which is a reentrancy point.

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