Your First Contract

One line, and the body between its braces is empty. This is the coin slot: the function that runs when plain ETH arrives with no instructions attached. Its name is receive, and the empty body means accepting silently is all it does.

Three words sit on this line: receive, external, payable. Ben walks up to the pig and sends 1 ETH, plain, nothing else. Exactly one of those words is the one that lets the contract accept his ETH. Which?

The pig weighs itself. The phrase address(this).balance is the contract reading its own ETH balance: this means this very contract, and balance is what it currently holds. The phrase returns (uint256) names what comes back to the caller: one whole number.

One new word does the promising. Function first: a marker that swears this function only reads, changes nothing, moves nothing. The name: view. Reading costs the chain nothing, so anyone may call progress for free, forever, and simply watch the pig fill up.

The last function, and the heart of the engraving. One word to meet properly first. Function first: a statement that checks a condition, and if the condition is false, stops everything and rewinds it, as if the call never happened. The name: require.

That is the language's whole rulebook in one word. No judge, no appeal: the machine enforcing its own text. Two requires and one payout make up smash. Tap each of the three lines to read it as a rule engraved on the glass.

Now watch the rules meet a person. Ben dropped 1 ETH into the pig last week. Today he wants it back, and the goal is nowhere near reached. He calls smash. The call reaches line 20, and the first require asks its question.

msg.sender is Ben. owner is Ana. The condition is false. Before reading on, decide exactly what happens next, because this one scene is require semantics in full.

Look at the whole board again. Every line is lit, and you can read the entire engraving aloud in six sentences: paperwork, box and memory, birth, coin slot, scale, rules. That is the whole machine, pragma to closing brace.

You just read a complete, real contract. Not a diagram of one, not an excerpt: the contract, every line, and nothing in it is a mystery to you anymore. The glass pig keeps no secrets from someone who reads.

A fair question before we close. Tomorrow Ana opens a different contract, a real one from a live protocol, five hundred lines long. Will every Solidity file now yield to you the way this one did? Find the honest edge of what you just learned.

This lesson is the prototype of a full season: twenty four real contracts, each one read exactly like this, line by line, predictions before reveals, the lens walking down the board. The vocabulary grows every week. The method never changes.

It ends with you opening a verified contract you have never seen and reading it cold, unaided. Today you read your first. The glass pig was the beginning.