Day 44 — Solidity Inheritance (Protocol-Safe Design)

This project demonstrates safe-to-extend inheritance in Solidity.

Instead of making public functions virtual, we lock core state transitions and expose controlled extension points via internal hooks.

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Architecture

BaseVault

• deposit() is NOT virtual
• Extension allowed only via:
  • _beforeDeposit()
  • _afterDeposit()

Invariant:

address(this).balance == totalDeposits

The state transition is fixed:

1. Before hook
2. Accounting update
3. Event emission
4. After hook

This prevents child contracts from:

• breaking accounting
• changing state transition order
• introducing unsafe interactions

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PointsVault

Overrides _afterDeposit() to award points.

Core accounting remains untouched.

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Key Concepts

• Storage linearization in inheritance
• Explicit virtual / override
• Hook pattern vs overriding public functions
• Invariant protection
• Reduced attack surface

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Tests

• Verifies deposit event
• Verifies accounting update
• Verifies hook-based extension

Includes force-send edge case (selfdestruct) proving that ETH can bypass public state transitions and break naive invariants.

Run:

npx hardhat test