Explore the foundational concepts behind Ethereum’s leading token standards: ERC-20, ERC-721, and ERC-1155. These standards are crucial for understanding how digital assets function on the blockchain, from cryptocurrencies to unique digital collectibles.

ERC-20: The Standard for Fungible Tokens

ERC-20 tokens are the most common type, representing fungible assets—meaning each token is identical to another and interchangeable, much like traditional currency. They are widely used for cryptocurrencies, utility tokens, and stablecoins.

Key Functions:
* totalSupply(): Reveals the total number of tokens in circulation.
* balanceOf(address account): Shows an account’s token balance.
* transfer(address to, uint256 amount): Moves tokens from one address to another.
* approve(address spender, uint256 amount): Grants permission for another address to spend a specific amount of your tokens.
* allowance(address owner, address spender): Checks the amount a spender is approved to use from an owner’s account.
* transferFrom(address from, address to, uint256 amount): Transfers tokens using a pre-approved allowance.
* Internal Functions (_mint, _burn): Handle the creation and destruction of tokens within the contract.

ERC-721: Pioneering Non-Fungible Tokens (NFTs)

ERC-721 tokens are unique, non-fungible assets, meaning each token is distinct and has a specific identity. This standard revolutionized digital ownership, enabling the creation of unique digital collectibles, art, and virtual land.

Key Functions:
* balanceOf(address owner): Returns the number of NFTs an address owns.
* ownerOf(uint256 tokenId): Identifies the owner of a specific NFT.
* approve(address to, uint256 tokenId): Authorizes another address to transfer a particular NFT.
* getApproved(uint256 tokenId): Returns the approved address for a specific NFT.
* setApprovalForAll(address operator, bool approved): Allows an operator to manage all your NFTs.
* isApprovedForAll(address owner, address operator): Checks if an operator has full management rights.
* transferFrom(address from, address to, uint256 tokenId): Transfers ownership of a single NFT.
* safeTransferFrom(address from, address to, uint256 tokenId): Safely transfers an NFT, ensuring the recipient can handle it.
* Internal Functions (_mint, _burn): Create and destroy unique NFTs.

ERC-1155: The Multi-Token Standard

ERC-1155 is a more advanced standard that allows a single contract to manage both fungible and non-fungible tokens, as well as semi-fungible tokens. It offers greater efficiency and flexibility, particularly for gaming and metaverse applications where a variety of item types are needed.

Key Functions:
* balanceOf(address account, uint256 id): Checks an account’s balance for a specific token ID.
* balanceOfBatch(address accounts, uint256 ids): Retrieves multiple token balances in one call.
* setApprovalForAll(address operator, bool approved): Grants or revokes an operator’s permission to manage all your tokens (of any type).
* isApprovedForAll(address account, address operator): Confirms if an operator can manage all tokens for an account.
* safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes data): Safely transfers a specific quantity of a single token type.
* safeBatchTransferFrom(address from, address to, uint256 ids, uint256 amounts, bytes data): Safely transfers multiple token types simultaneously.
* Internal Functions (_mint, _mintBatch, _burn, _burnBatch): Facilitate the creation and destruction of single or multiple token types efficiently.

These three Ethereum token standards form the backbone of the decentralized ecosystem, enabling a vast array of digital assets and applications. Understanding their core functionalities is key to navigating the world of blockchain and cryptocurrencies.