Mastering Blockchain - Second Edition

Inheritance

Inheritance is supported in Solidity. The is keyword is used to derive a contract from another contract. In the following example, valueChecker2 is derived from the valueChecker contract. The derived contract has access to all non-private members of the parent contract:

pragma solidity ^0.4.0;  
contract valueChecker 
{ 
    uint8 price = 20; 
    event valueEvent(bool returnValue);  
    function Matcher(uint8 x) public returns (bool) 
    { 
        if (x>=price) 
        { 
            valueEvent(true);  
            return true; 
        } 
    } 
} 
contract valueChecker2 is valueChecker 
{ 
    function Matcher2() public view returns (uint) 
    { 
        return price+10; 
    } 
} 

In the preceding example, if the uint8 price = 20 is changed to uint8 private price = 20, then it will not be accessible by the valueChecker2 contract. ...