solidity-learnings

notes and links for solidity

Truffle setup

npm install truffle -g
mkdir MyContract && cd MyContract
truffle init . 
truffle create contract MyContract
truffle create test MyContract

create a one new or edit default migration file after adding a contract.

Truffle testing

truffle compile 
truffle test
truffle develop
truffle(develop)> migrate 
truffle(develop)> migrate --reset # for redeployment 

# load contract instance and interact with contract 
truffle(develop)> let instance = await MyContract.deployed()
# call function with args 
truffle(develop)> instance.myPublicFunction(args) 
# call from other accounts
truffle(develop)> instance.myPublicFunction({from: accounts[2]})
# call payable functions
truffle(develop)> instance.myPublicFunction({value: web3.utils.toWei("1", "ether")}) 

Solidity

Functions visibility

• Private - can only be called from inside smart contract
• Internal - can only be called from inside smart contract and inherited contracts
• External - can only be called from outside smart contract -- [inherited contracts -> TBA]
• Public - can be called from anywhere

function myFunction() <visibility specifier> returns (bool) {
    return true;
}

Functions state mutability

• View - RO, can only reads from chain
• Pure - doesn’t interact with chain,
• Payable - [TBA]

function myFunction() public view returns (bool) {
    return true;
}

Functions modifiers

Adds conditions to execute before, after or while executing a function.

// verifies caller before executing functions 
modifier onlyOwner {
    require(msg.sender == owner, "Only owner can call this function.");
    _;
}
// verifies result after function has computed value
modifier validateResult(uint computedValue) {
    _;
    require(computedValue == PI, "Invalid Result");
}

function myFunction() public onlyOwner validateResult(value) view returns (bool) {
    return true;
}

Special Functions

Constructors

• Optional
• Executes on contract creation

Init function

For clones, proxies or libraries an init function is defined instead of a constructor. Should be used generally with a single init or reentrant guard.

Fallback function

• Nameless function
• Called when other contracts call wrong function name
• Called when eth is transferred to this contract
• Can only be defined once per contract
• Must be external / public

Global variables

Generally language keywords can be described in three categories

1. tx
2. Msg
3. Block

tx.origin vs msg.sender

1. Alice calls Smart Contract A => {tx.origin: Alice, msg.sender: Alice}
2. Smart Contract A calls Smart Contract B => {tx.origin: Alice, msg.sender: Smart Contract A}