Ethereum-Solidity Quiz Q23: What is C3 Linearization in smart contract inheritance?

#web3 #ethereum #solidity #blockchain

C3 linearization is an algorithm that determines the order in which parent contracts are searched when a derived contract inherits from multiple parents. It's also called the Method Resolution Order (MRO).

It solves the Diamond Problem, where a contract inherits from two parents that both inherit from the same grandparent. Without C3, the compiler wouldn't know which version of a shared function to execute.

1. Fundamental Rule

The most important thing to remember for Solidity is the direction of inheritance - from "most base-like" to "most derived."

In the declaration contract Child is A, B, B is considered "more derived" than A. If both have the same function, the version in B will be checked first.

2. How the Search Order Works

When you call a function or use the super keyword, Solidity follows a flattened list generated by the C3 algorithm. The search follows these steps:

Start at the Child: Check if the function is defined in the current contract.

Move Right-to-Left: Check the parent contracts in the order they were listed, starting from the right-most one.

Go Up the Hierarchy: Move up to the grandparents only after all immediate parents have been checked.

Example: The "Diamond" Chain

contract A {
    function foo() public virtual { /* Logic A */ }
}

contract B is A {
    function foo() public virtual override { super.foo(); }
}

contract C is A {
    function foo() public virtual override { super.foo(); }
}

// Order: A (base) -> B -> C (most derived)
contract D is B, C {
    function foo() public override(B, C) {
        super.foo(); 
    }
}

The Linearization of D is: [D, C, B, A]