Speedrun Ethereum

Speedrun Ethereum is a hands-on series of challenges designed to help you learn by building. Build @buidlguidl @austingriffith

[Speedrun Ethereum @Speedethereum]

https://t.co/H26QSKUVYp

[Speedrun Ethereum @Speedethereum]

10 Challenge Spotlights, one for every challenge on Speedrun Ethereum.

Tokenization. Crowdfunding. Token Vendor. Dice Game. DEX. Oracles. Lending. Stablecoins. Prediction Markets. ZK Voting.

That's a full cycle. Which one was your favorite?

[Speedrun Ethereum @Speedethereum]

🧵 How to Safely Call Other Contracts in Solidity

Smart contracts rarely live alone. Most real-world dApps rely on contract-to-contract communication.

But every call is a potential risk.

Here’s how to do it securely 👇

[Speedrun Ethereum @Speedethereum]

6/
🧪 Secure Vendor Example

A real-world pattern:

- Buyer approves ERC20 token
- Vendor pulls with transferFrom()
- Sends reward token
- Uses nonReentrant for safety
- Follows CEI

[Speedrun Ethereum @Speedethereum]

🧵 How to Safely Call Other Contracts in Solidity

Smart contracts rarely live alone. Most real-world dApps rely on contract-to-contract communication.

But every call is a potential risk.

Here’s how to do it securely 👇

[Speedrun Ethereum @Speedethereum]

5/
🔁 Reentrancy is Real
Attackers can re-enter your contract mid-function and drain funds.

💡 Defend with:

- Checks-Effects-Interactions pattern
- OpenZeppelin ReentrancyGuard

[Speedrun Ethereum @Speedethereum]

Foundry support just shipped on Speedrun Ethereum 🔨

Pick your stack when you start a challenge: Hardhat or Foundry.

Try it on the first challenge:
npx [email protected] -e challenge-tokenization challenge-tokenization

Available for challenges 0 to 4. More coming soon.

[BuidlGuidl.eth @buidlguidl]

Challenge 5: Oracles.

The exercise:
• Your contract needs off-chain data (a price, a weather feed, a score)
• Solidity can only see on-chain state
• An oracle bridges the gap, and becomes a trust anchor you have to reason about

[BuidlGuidl.eth @buidlguidl]

Two ways to declare a value that never changes:

• `constant` — inlined at compile time. Value has to be known before deploy.
• `immutable` — set once in the constructor. Stored in bytecode, not a storage slot.

Reading either costs ~3 gas. Reading a storage variable costs ~100 (warm) or ~2100 (cold). Use one of these whenever you can.

[BuidlGuidl.eth @buidlguidl]

Challenge 4: Build a DEX.

The exercise:
• Constant-product AMM from scratch (`x * y = k`)
• Provide liquidity, earn swap fees
• Swap against your own pool
• Under 50 lines of Solidity at the core