Solidity Principles

Progressive smart contract exercises exploring storage patterns, access control, and on-chain data structures in Solidity.

Storage Contracts

Each version builds on the previous one, adding a new concept while keeping the code simple.

Contract	Concept	Key Addition
Storage1	Elementary operations	pure function (two args) and view function (one arg) for multiplication
Storage2	Gas cost observation	Same logic as Storage1, used to compare gas between set() and read-only calls
Storage3	Error handling	Overflow, underflow and division-by-zero checks with require
Storage4	Data type cost comparison	Separate uint8, uint16, uint128, uint256 variables to compare gas
Storage5	Read restriction	Only the last writer can read the value; others receive 0
Storage6	Constructor	Initial value set on deployment via constructor(uint)
Storage7	Owner-only writes	onlyOwner modifier restricts set() to the deployer

Agenda Contracts

On-chain contact book where each entry holds an ETH address and a name. Versions add progressive access control and search capabilities.

Contract	Concept	Key Addition
Agenda1	Basic entries	Global contact list with addContact and getContact
Agenda2	Per-user storage	mapping(address => Contact[]) gives each user their own book
Agenda3	Edit and delete	editContact and deleteContact with swap-and-pop pattern
Agenda4	Time-limited delegation	grantAccess(delegate, seconds) for read-only access with expiry
Agenda5	Search	searchByAddress and searchByName using keccak256 for string comparison

Storage Design

The StorageContracts file demonstrates how Solidity handles state writes versus read-only calls. Writing to storage (SSTORE) costs around 20,000 gas for a cold slot, while pure and view functions cost zero gas when called externally. Storage4 shows that the EVM always operates on 256-bit words, so smaller types like uint8 do not reduce gas per individual slot.

Access Control Model

The AgendaContracts file explores three levels of access control. Per-user isolation is achieved through msg.sender as the mapping key, ensuring no user can access another's data. Time-limited delegation uses block.timestamp to auto-expire permissions. Owner-only restriction in Storage7 uses a modifier that checks msg.sender against the deployer address stored at construction.

System Architecture

Component	Role
Remix IDE	Development environment for compiling, deploying and testing all contracts
Solidity Compiler 0.8+	Provides built-in checked arithmetic (overflow/underflow protection)
EVM (JavaScript VM)	Local blockchain used in Remix for testing without real gas costs
GitHub	Version control and repository hosting

Technology Stack

• Language: Solidity 0.8+
• IDE: Remix IDE (browser-based)
• Runtime: EVM-compatible JavaScript VM (Remix default)
• Version Control: Git, GitHub

Key Features

1. Incremental contract versions — each file progresses from basic to advanced, one concept at a time
2. Pure vs view comparison — demonstrates the gas difference between state-reading and stateless functions
3. Built-in overflow protection — leverages Solidity 0.8 checked arithmetic instead of SafeMath
4. Swap-and-pop deletion — avoids gaps in dynamic arrays when removing contacts
5. Time-based delegation — read-only access expires automatically using block.timestamp
6. String search via hashing — uses keccak256 to compare strings since Solidity lacks native string equality

Testing Strategy

All contracts are tested manually in Remix IDE using the JavaScript VM environment. Each contract is deployed, and functions are called with different accounts from the Remix account selector to verify access control. Gas costs are compared by reading the transaction and execution cost fields in the Remix console. Error cases (overflow, division by zero, unauthorized access) are tested by triggering reverts and confirming the expected error messages.

Project Setup

1. Open Remix IDE

2. Create the contract files in the root of your workspace:

   StorageContracts.sol
   AgendaContracts.sol
   

3. Select compiler version 0.8.0 or higher and compile both files

4. In the Deploy tab, select Remix VM as the environment

5. Deploy any contract and interact with it using the generated UI

---

Built for Ethereum / EVM-compatible chains.