It is very similar to single inheritance, but the difference is that it has levels of the relationship between the parent and the child. The child contract derived from a parent also acts as a parent for the contract which is derived from it.
Example: In the below example, contract A is inherited by contract B, contract B is inherited by contract C, to demonstrate Multi-level Inheritance.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
// Defining parent contract A
contract A {
string internal x;
string a = "Multi";
string b = "Level";
// Defining external function to return concatenated string
function getA() external {
x = string(abi.encodePacked(a, b));
}
}
// Defining child contract B inheriting parent contract A
contract B is A {
string public y;
string c = "Inheritance";
// Defining external function to return concatenated string
function getB() external payable returns (string memory) {
y = string(abi.encodePacked(x, c));
}
}
// Defining child contract C inheriting parent contract A
contract C is B {
function getC() external view returns (string memory) {
return y;
}
}
// Defining calling contract
contract caller {
// Creating object of child C
C cc = new C();
// Defining public function to return final concatenated string
function testInheritance() public returns (string memory) {
cc.getA();
cc.getB();
return cc.getC();
}
}Output:
when we call the testInheritance function, the output is "MultiLevelInheritance".