Solidity Notes

state variables

• https://docs.soliditylang.org/en/latest/types.html
• https://docs.soliditylang.org/en/latest/contracts.html#visibility-and-getters

contract MultisigTutorial {
  	address[] public owners;
	mapping(address => bool) public isOwner;
	uint public numConfirmationsRequired;
}

1. owners: An array containing the addresses of all owners of the multi-signature wallet.
2. isOwner: A mapping indicating whether an address is an owner.
3. numConfirmationsRequired: The number of confirmations required for a transaction.

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modifier

special keyword to amend the behavior of functions

mapping(address => bool) public isOwner;

modifier onlyOwner() {
  require(isOwner[msg.sender], "not owner");
  _;
}

onlyOwner modifier ensures that only owners can execute a function. It does this by checking whether the address of the caller is an owner.

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constructor

defines a function that executed only once during the deployment of the contract.

uint public numConfirmationsRequired;

constructor(address[] memory _owners, uint _numConfirmationsRequired) {
	require(_owners.length > 0, "owners required");
  	require(
    	_numConfirmationsRequired > 0 &&
      	_numConfirmationsRequired <= _owners.length,
      	"invalid number of required confirmations"
    );
  
  for (uint i = 0; i < _owners.length; i++) {
  	address owner = _owners[i];
    
    require(owner != address(0), "invalid owner");
    require(!isOwner[owner], "owner not unique");
    
    isOwner[owner] = true;
    owners.push(owner);
  }

  numConfirmationsRequired = _numConfirmationsRequired;
}

It initializes essential parameters, in this case, the list of owners and the required number of confirmations. (temporarily assign to isOwner for assure uniqueness)

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view

Functions can be declared view in which case they promise not to modify the state.

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Order of functions

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Contract Elements Order

1. pragma
2. import
3. event
4. error
5. interface
6. library
7. contract

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Orders in each [ contract / library / interface ]

1. Type declarations
2. State variables
3. event
4. error
5. modifier
6. function

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Orders of functions

1. constructor
2. receive function (if exists)
3. fallback function (if exists)
4. external
5. public
6. internal
7. private

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Function Types

function (<parameter types>) {internal | external} [pure | view | payable] [returns (<return types>)]