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ABI (Application Binary Interface) is a JSON file that contains all the information (functions/params/return values) to interact with the smart contract

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Ethereum Developer Masterclass

Key takeaways from Udemy's course 'Ethereum Developer Masterclass: Build Real World Projects'.
Ethereum
Blockchain
Solidity
Truffle
Development
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Solidity is the most popular programming language for building Ethereum dApps
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Solidity compiles to bytecode that runs on the EVM -- Ethereum Virtual Machine
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Solidity accepts multiple inheritance
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Solidity accepts most of the primitive types except float number
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Solidity accepts if/else and for/while statements
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Smart contracts are immutable -- changes are not possible
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An Ethereum Blockhain node implements the Ethereum Protocol and connects to other nodes -- it gives you access to the blockchain
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TestRPC library simulates the Ethereum Network and is used to unit test smart contracts since mining is simulated and takes almost no time
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MetaMask is a plugin for Chrome, can sign transactions and doesn't download the blockchain -- it's not a full node nor a light client
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A transaction, when processed and validated by miners, go to the blockchain. It updates the state and costs ETH (gas)
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Calls are local, read-only and free
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Transactions cost ETH (gas to miners), it's a write operation, it changes the state of the blockchain
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Transactions between Contracts are mined in the same block and returned all together
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The Genesis block can be configured in a file named genesis.json or config.json
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We can save the MNEMONIC pass phrase given by testrpc to always generate the same accounts: testrpc -m 'MNEMONIC'
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Access to the blockchain is a normal REST interface that uses JSON
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Web3.js is a JS library that makes it easier to interact with the Ethereum Blockchain
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Ethereum Wallet is a dApp in pure HTML/JS that uses Web3.js to manage our accounts
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geth is the the command line interface for running a full ethereum node implemented in Go
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MIST is a 'browser' that uses Web3.js to interact with geth node
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For Linux/MacOs we need to tell MIST where our private geth.ipc file is located
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Remix is a web IDE for smart contract development
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Truffle is a Smart Contract development framework that makes testing and deployment easy. It uses Mocha and Chai and works with Promises
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ERC20 Tokens is a standard pattern for tokens in the Ethereum Network
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ERC20 is a set of functions used as interface
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An ICO is nothing else than deploying a smart contract
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ICO - Initial Coin Offering is usually just a Smart Contract offering tokens
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Libraries are reusable contracts, they're not inherited
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Truffle works with EthPM which is a Package Manager only for Ethereum, similar to NPM
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address.transfer() is preferrable over address.send() since it delegates gas, exceptions and rolls back in case of any issue
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You can only throw an exception in Solidity, there's no message and no catch block
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assert() and require() are better ways of throwing exceptions
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In case of failure, assert() consumes all the gas whereas require() returns all gas
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Everything is public on the blockchain, even local and private variables
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Random numbers depend on miners, be careful
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Be careful with loops since it can consume all the gas available
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Maximum call-stack in the Ethereum network is 1024
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msg.sender vs tx.origin -- never use tx.origin for authorization to avoid unauthorized access
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Restrict the amount of Ether or tokens -- just in case
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mappings in Solidity are like hash tables
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The value of a mapping can be of any type, except of a mapping
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The key of a mapping can be anything except: mapping, dynamic array, contract, enum and struct
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mapping(keyType => valueType) name
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mapping: all values are initialized by default, it doesn't have a length, it's not possible to retrieve list of values or keys
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Struct is like a Java class, but you don't need to use the new keyword to instantiate it
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msg.sender is a global variable and its type is 'address'
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In order to compare strings, they must be converted to bytes. A commonly used version of equals() is available on the internet
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truffle test: uses Mocha, you need to required the contract as a JS object, all calls return promises, transactions don't need to be mined
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