ERC to NEP Migration Pitfalls

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Common ERC-20 → NEP-17 Mistakes

1. Keeping 2-parameter transfer:

   // ❌ ERC-20 style — won't be detected as NEP-17
   function transfer(address to, uint256 amount) public returns (bool) { ... }
   
   // ✅ NEP-17 style — 4 parameters
   function transfer(address from, address to, uint256 amount, Any calldata data)
       public returns (bool) { ... }

2. Using msg.sender for authorization:

   // ❌ EVM pattern
   require(msg.sender == from, "unauthorized");
   
   // ✅ Neo pattern — cryptographic witness verification
   require(Runtime.checkWitness(from), "unauthorized");

3. Keeping approve/allowance:

   // ❌ Not part of NEP-17 spec — compiler warns W103
   function approve(address spender, uint256 amount) public { ... }
   
   // ✅ Remove — witness model replaces approvals entirely

4. Missing onNEP17Payment callback:

   // ❌ EVM pattern
   receive() external payable { ... }
   
   // ✅ NEP-17 callback — required for contracts receiving tokens
   function onNEP17Payment(address from, uint256 amount, Any calldata data) external { ... }

Common ERC-721 → NEP-11 Mistakes

1. Using uint256 token IDs instead of bytes32
2. Keeping transferFrom instead of 3-param transfer
3. Missing required tokensOf() and properties() methods
4. Missing decimals() returning 0 for indivisible NFTs

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