零点课堂 | What Are Flash Loans in DeFi? (3)
The catch? A flash loan must be repaid in the same transaction. That's not very intuitive at all, but that's only because we're used to a typical transaction format where funds move from one user to another. Like when you pay for goods or services, or deposit tokens into an exchange.
However, if you know a bit about Ethereum, you'll know that the platform is pretty flexible – that's why some call it programmable money. In the case of a flash loan, you can think of your transaction "program" as being made up of three parts: receive the loan, do something with the loan, repay the loan. And it all happens in a flash!
Let's just attribute it to the magic of blockchain technology. The transaction gets submitted to the network, temporarily lending you those funds. You can do some stuff in part two of the transaction. Do whatever you want, so long as the funds are back in time for part three. If they're not, the network rejects the transaction, meaning that the lender gets their funds back. Actually, as far as the blockchain is concerned, they always had the funds.
That explains why the lender doesn't require collateral from you. The contract to repay is enforced by code.
But what's the point?
At this stage, you're probably wondering why you'd take out a flash loan. If all of this occurs in a single transaction, you can't exactly purchase a Lambo, can you?
Well, that's not really the goal here. Let's focus on part two of the transaction described previously, where you do something with the loan. The idea is to feed the funds into a smart contract (or chain of contracts), flip a profit, and return the initial loan at the end of the transaction. As you can see, the point of flash loans is to profit.