This topic is about Solidity – Inheritance.
Inheritance is a way to extend functionality of a contract. Solidity supports both single as well as multiple inheritance. Following are the key highlighsts.
- A derived contract can access all non-private members including internal methods and state variables. But using this is not allowed.
- Function overriding is allowed provided function signature remains same. In case of difference of output parameters, compilation will fail.
- We can call a super contract’s function using super keyword or using super contract name.
- In case of multiple inheritance, function call using super gives preference to most derived contract.
Example
pragma solidity ^0.5.0;
contract C {
//private state variable
uint private data;
//public state variable
uint public info;
//constructor
constructor() public {
info = 10;
}
//private function
function increment(uint a) private pure returns(uint) { return a + 1; }
//public function
function updateData(uint a) public { data = a; }
function getData() public view returns(uint) { return data; }
function compute(uint a, uint b) internal pure returns (uint) { return a + b; }
}
//Derived Contract
contract E is C {
uint private result;
C private c;
constructor() public {
c = new C();
}
function getComputedResult() public {
result = compute(3, 5);
}
function getResult() public view returns(uint) { return result; }
function getData() public view returns(uint) { return c.info(); }
}
Run the above program using steps provided in Solidity First Application chapter. Run various method of Contracts. For E.getComputedResult() followed by E.getResult() shows −
Output
0: uint256: 8
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