Tokens não fungíveis ERC-721 (NFTs)

Welcome to the world of Non-Fungible Tokens (NFTs)! Unlike regular money or cryptocurrencies, NFTs are unique digital items.

Think of them like rare collectibles or one-of-a-kind art pieces, but entirely digital. Each NFT has distinct properties and cannot be replaced by another.

On Ethereum, NFTs are defined by a standard called ERC-721. This standard is a set of rules that smart contracts must follow to create, manage, and transfer unique tokens.

It ensures that all compliant NFTs work similarly across different platforms, making them interoperable.

Every ERC-721 token has a unique Token ID (a large number). This ID distinguishes it from all other NFTs, even those from the same collection.

The standard also defines functions to track ownership:

• ownerOf(uint256 tokenId): Returns the address that owns a specific NFT.
• balanceOf(address owner): Returns the number of NFTs an address owns from that contract.

Creating an ERC-721 contract from scratch can be complex. Luckily, OpenZeppelin provides battle-tested, secure implementations.

We can simply import their contracts and build upon them. This saves time and reduces the risk of vulnerabilities.

Here's a basic structure for an ERC-721 contract using OpenZeppelin. It defines a name and symbol for our NFT collection in the constructor.

We'll add a minting function next.

To bring new NFTs into existence, we use a process called minting. The _safeMint function (provided by OpenZeppelin's ERC721) creates a new token and assigns it to an owner.

Let's add a public mint function to our contract to create new NFTs.

An NFT's value often comes from what it represents (an image, a song, a game item). This information, called metadata, isn't stored directly on the blockchain due to cost.

Instead, the ERC-721 standard includes a tokenURI(uint256 tokenId) function. This function returns a URL pointing to a JSON file that describes the NFT's metadata (e.g., name, description, image URL).

Once an NFT is minted, it can be transferred between owners. The ERC-721 standard includes functions for this:

• transferFrom(address from, address to, uint256 tokenId): Transfers ownership of tokenId from from to to.
• safeTransferFrom(...): A safer version that checks if the recipient contract can receive NFTs.

These functions ensure only the current owner or an approved address can initiate a transfer.

Sometimes, you might want to allow another address (like a marketplace) to transfer your NFT on your behalf. This is done using approvals.

The approve(address to, uint256 tokenId) function lets you grant permission to another address to to manage a specific tokenId. This is crucial for decentralized exchanges and other dApps.

Let's test your understanding of ERC-721 NFTs. Select all statements that are true.

You've explored the fascinating world of ERC-721 Non-Fungible Tokens!

• NFTs are unique digital assets, unlike fungible cryptocurrencies.
• The ERC-721 standard defines how these unique tokens are created and managed on Ethereum.
• Key features include unique Token IDs, ownership tracking, minting, and linking to off-chain metadata via tokenURI.
• OpenZeppelin contracts simplify ERC-721 development.

NFTs are a cornerstone of digital ownership and are used in art, gaming, and many other applications!