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solidity.md

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Blockchain class notes

Gas

  1. How exactly does gas prevent infinite loops
  2. How do you pay for mistakes made
  3. What exactly qualifies as a “mistake”?

Smart Contract Tools

  1. If web3js is poorly written, why is there no alternative?

Other Blockchains

  1. What’s the major differences between Ethereal and the other blockchains (EOS, Neo, Lisk)?

Solidity

  1. If they create a $117000000 million bug, are people weary of still using solidity?
  2. Are there alternatives?

Other

  1. What’s an ERC20 token?

Notes

Types bool: 0 or 1 uint address: wallet or ethereum address string: always surrounded by double-quotes

Structures array: Series of object that are the same size and type mapping: Hash tables between two different types Struct: Used to define new types enum: Used to create a user-defined type

Functions Fallback functions: default functions that smart contract goes to when no data is provided Constructor: Runs once immediately after deployment

Unique keywords msg.sender: Address of person/contract calling function msg.value: Amount of ETH sent in the transaction block.number: Number of block order in Ethereum block.timestamp: Time the block was mined (~15 sec/block)

Accessibility external: Can be called by other contracts and via transactions internal: Can be called from within its own contract or derived contracts public: Can be called externally or internally private: Can be called from within its own contract

Error Handling require: To check conditions on input, returns leftover gas assert: To check internal errors, consumes all gas in transaction

Modifiers Change the behavior of the function they’re attached to Check a condition before running a function onlyOwner: Permission control payable: Allows for interaction with ether view: Doesn’t modify state pure: Doesn’t read from nor modify state

Event Stores arguments that functions take and stores in logs emit: Broadcasts arguments to listeners in user interface indexed: Attribute that allows arguments to be searched for

Optimization Each line of code that is written costs gas Gas costs real-world money Sloppy code becomes expensive very quickly