Mappings in Solidity act as hash tables that store key-value pairs, similar to dictionaries in Python or objects in JavaScript. They provide instant value lookup using unique keys and are gas-efficient for smart contract storage.

Basic mapping syntax:

mapping(keyType => valueType) visibility variableName;

Example of a token balance mapping:

mapping(address => uint256) public balances;

Key features of Solidity mappings:

• Zero-value initialization: All possible keys exist by default with zero/null values
• No size tracking: Mappings don't store length or key lists
• Key immutability: Keys must be value types, not reference types
• Direct key access: No iteration through keys possible
• Gas efficiency: Optimized for single-value lookups

Common use cases:

• Token balances
• User permissions
• Game state storage
• Voting systems
• Contract ownership records

Best practices:

1. Always validate input data before storing
2. Use appropriate key and value types
3. Consider gas costs for complex operations
4. Document mapping purposes clearly
5. Implement getter functions for better access control

Note: Unlike arrays, mappings cannot be iterated over directly. If you need to track or iterate through stored values, maintain a separate array of keys.

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