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Smart contracts and the EVM

Lesson 3 of 8
By the end of this lesson you’ll be able to say what a smart contract can and can’t do, find out whether one can be changed after launch and by whom, and read its code and settings on a block explorer without writing a line of programming.
A collage of a giant suit of armor seen from behind, its back plate open like a door. A tiny figure in blue climbs a ladder into the hollow, while a tiny man in a dark suit walks away across the flagstones.

What a smart contract is

ethereum.org’s definition is short: a smart contract is “simply a program that runs on the Ethereum blockchain.” Its favorite comparison is a vending machine.

Put in the right coins, press the right button, and “a certain output is guaranteed.” Nobody stands behind the counter.

Contracts are “not controlled by a user, instead they are deployed to the network and run as programmed.” “Anyone can write a smart contract and deploy it to the network,” which is why there are so many and why quality varies so much. And “Smart contracts cannot be deleted by default, and interactions with them are irreversible,” so a bug in a contract is a bug for as long as money sits in it.

Runs as programmed
No user controls it once it’s deployed
Open to anyone
Anyone can write and deploy one
Hard to undo
No deleting by default, and no reversing what it did
What every contract shares

Every token, every exchange that runs without a company, every lending pool and every layer 2 bridge is a contract or a set of them. When you “use DeFi,” you are sending transactions to programs.

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