Notes

• Maps are created with the syntax mapping(keyType => valueType).
• The keyType can be any built-in value type, bytes, string, or any contract.
• valueType can be any type including another mapping or an array.
• Mappings are not iterable.

Code

Compile and deploy the code block below:

solidity
Mapping.sol
Copy
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Mapping {
   // Mapping from address to uint
   mapping(address => uint) public myMap;

   function get(address _addr) public view returns (uint) {
       // Mapping always returns a value.
       // If the value was never set, it will return the default value.
       return myMap[_addr];
   }

   function set(address _addr, uint _i) public {
       // Update the value at this address
       myMap[_addr] = _i;
   }

   function remove(address _addr) public {
       // Reset the value to the default value.
       delete myMap[_addr];
   }
}

contract NestedMapping {
   // Nested mapping (mapping from address to another mapping)
   mapping(address => mapping(uint => bool)) public nested;

   function get(address _addr1, uint _i) public view returns (bool) {
       // You can get values from a nested mapping
       // even when it is not initialized
       return nested[_addr1][_i];
   }

   function set(address _addr1, uint _i, bool _boo) public {
       nested[_addr1][_i] = _boo;
   }

   function remove(address _addr1, uint _i) public {
       delete nested[_addr1][_i];
   }
}