Index

Solidity

  1. types
  2. External
  3. Library
    1. self in Library
    2. using * for
    3. self example
  4. interfaces
  5. import
  6. msg.value
  7. Handling ether
  8. Erc20 token in contract
  9. assembly
  10. Enum
  11. memory, storage, calldata
  12. Array Pushing
  13. length in array
  14. Struct array
  15. mapping
  16. bytes and string
  17. uint to bytes32
  18. returns with name
  19. score voting
  20. Tests
    1. Async Tests
    2. Hooks

mapping



pragma solidity >=0.4.0 <0.7.0;

contract MappingExample {
    mapping(address => uint) public balances;

    function update(uint newBalance) public {
        balances[msg.sender] = newBalance;
    }
}

contract MappingUser {
    function f() public returns (uint) {
        MappingExample m = new MappingExample();
        m.update(100);
        return m.balances(address(this));
    }
}


// For a financial app, storing a uint that holds the user's account balance:
mapping (address => uint) public accountBalance;
// Or could be used to store / lookup usernames based on userId
mapping (uint => string) userIdToName;

A mapping is essentially a key-value store for storing and looking up data. In the first example, the key is an address and the value is a uint, and in the second example the key is a uint and the value a string.