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Update EIP-721: Use latest version of solidity and remove caveats #5887

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Update EIP-721: Use latest version of solidity and remove caveats #5887

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19 changes: 4 additions & 15 deletions EIPS/eip-721.md
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Expand Up @@ -41,12 +41,12 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "S
**Every ERC-721 compliant contract must implement the `ERC721` and `ERC165` interfaces** (subject to "caveats" below):

```solidity
pragma solidity ^0.4.20;
pragma solidity ^0.8.17;
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In safeTransferFrom:

TypeError: Data location must be "memory" or "calldata" for parameter in external function, but none was given.


/// @title ERC-721 Non-Fungible Token Standard
/// @dev See https://eips.ethereum.org/EIPS/eip-721
/// Note: the ERC-165 identifier for this interface is 0x80ac58cd.
interface ERC721 /* is ERC165 */ {
interface ERC721 is ERC165 {
/// @dev This emits when ownership of any NFT changes by any mechanism.
/// This event emits when NFTs are created (`from` == 0) and destroyed
/// (`to` == 0). Exception: during contract creation, any number of NFTs
Expand Down Expand Up @@ -179,7 +179,7 @@ The **metadata extension** is OPTIONAL for ERC-721 smart contracts (see "caveats
/// @title ERC-721 Non-Fungible Token Standard, optional metadata extension
/// @dev See https://eips.ethereum.org/EIPS/eip-721
/// Note: the ERC-165 identifier for this interface is 0x5b5e139f.
interface ERC721Metadata /* is ERC721 */ {
interface ERC721Metadata is ERC721 {
/// @notice A descriptive name for a collection of NFTs in this contract
function name() external view returns (string _name);

Expand Down Expand Up @@ -223,7 +223,7 @@ The **enumeration extension** is OPTIONAL for ERC-721 smart contracts (see "cave
/// @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
/// @dev See https://eips.ethereum.org/EIPS/eip-721
/// Note: the ERC-165 identifier for this interface is 0x780e9d63.
interface ERC721Enumerable /* is ERC721 */ {
interface ERC721Enumerable is ERC721 {
/// @notice Count NFTs tracked by this contract
/// @return A count of valid NFTs tracked by this contract, where each one of
/// them has an assigned and queryable owner not equal to the zero address
Expand All @@ -247,17 +247,6 @@ interface ERC721Enumerable /* is ERC721 */ {
}
```

### Caveats

The 0.4.20 Solidity interface grammar is not expressive enough to document the ERC-721 standard. A contract which complies with ERC-721 MUST also abide by the following:

- Solidity issue #3412: The above interfaces include explicit mutability guarantees for each function. Mutability guarantees are, in order weak to strong: `payable`, implicit nonpayable, `view`, and `pure`. Your implementation MUST meet the mutability guarantee in this interface and you MAY meet a stronger guarantee. For example, a `payable` function in this interface may be implemented as nonpayable (no state mutability specified) in your contract. We expect a later Solidity release will allow your stricter contract to inherit from this interface, but a workaround for version 0.4.20 is that you can edit this interface to add stricter mutability before inheriting from your contract.
- Solidity issue #3419: A contract that implements `ERC721Metadata` or `ERC721Enumerable` SHALL also implement `ERC721`. ERC-721 implements the requirements of interface ERC-165.
- Solidity issue #2330: If a function is shown in this specification as `external` then a contract will be compliant if it uses `public` visibility. As a workaround for version 0.4.20, you can edit this interface to switch to `public` before inheriting from your contract.
- Solidity issues #3494, #3544: Use of `this.*.selector` is marked as a warning by Solidity, a future version of Solidity will not mark this as an error.

*If a newer version of Solidity allows the caveats to be expressed in code, then this EIP MAY be updated and the caveats removed, such will be equivalent to the original specification.*

## Rationale

There are many proposed uses of Ethereum smart contracts that depend on tracking distinguishable assets. Examples of existing or planned NFTs are LAND in Decentraland, the eponymous punks in CryptoPunks, and in-game items using systems like DMarket or EnjinCoin. Future uses include tracking real-world assets, like real-estate (as envisioned by companies like Ubitquity or Propy). It is critical in each of these cases that these items are not "lumped together" as numbers in a ledger, but instead each asset must have its ownership individually and atomically tracked. Regardless of the nature of these assets, the ecosystem will be stronger if we have a standardized interface that allows for cross-functional asset management and sales platforms.
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