Maps in a solidity smart contract

This post has been updated click here

A map is like a hash table that allows you to save data on the Ethereum block chain in a key -> value pair relationship.

• It allows you to save data to the block chain
• You can retrieve this data in a function
• Maps are efficient for fast lookups
• You cannot get the size of a map
• Valid key types are string or byte which translates to a uint, bool and address
• Valid value types are any type

Use a map to keep track of data in one to one or one to many relationships.

Below is a sample of a solidity map in a smart contract.

pragma solidity >=0.7.0;

contract example {

    //new state variable called myExampleMap
         mapping (address => uint) public myExampleMap;


    //To read an item in the map you use the get function
        Function get(address _addr) public call  returns (uint) {
            Return myExampleMap[_addr];
            
        }     
    
    
    //To set an item in the map you use the set function
    Function set(address _addr, uint i) public call  returns (uint) {
             myExampleMap[_addr] = i;  
    
    }
    
    
    //To remove an item in the map you use the remove function
    Function remove(address _addr) public call  returns (uint) {
             Delete  myExampleMap[_addr];  
             
    }
    
}

try it in Remix

For more information read the docs.

Next Review – Enum in Solidity smart contracts