Lecture 13 - Ethereum

Code: ROM (Read-only memory) calldata: arguments

There are two types of instructions: Arithmetic including SHA3 and sys operations like create [contract], call [contract], and delegate call, etc.

CALL - called code is executed in the context of called contract CALLLOAD - called code is executed in the context of the current contract, msg.sender is calling contract DELEGATECALL - similar to callload except for msg.sender remains unchanged

Exceptions: leads to execution halting

Applications

  1. DB: NameCoin
  2. Auctions: decentralized eBay but since everything is public, requires commitments to have sealed bid auctions.

How to safely transfer funds

check-effects-interaction paradigm

Solidity
1
2
3
4
5
6
7

if (amount > 0) {  // check
    pendingReturns[msg.sender] = 0;  // effects
    if (!msg.sender.send(amount)) {  // interaction
        pendingReturns[msg.sender] = amount;
        return false;
    }
}

Events can be used for getting callbacks and executing a task in response to a change on the chain.

Use selfdestruct(beneficiary) to kill a contract and send the leftover money to the beneficiary.