[TIL] Solidity 02. Syntax

June 21, 2022

01. Syntax of Solidity

interface HelloWorldInterface {
    // private function is not visible so that cannot be used in the interface
    function helloWorld() external view returns (string memory);
    function setText(string memory newText) external;
}

// overriding the interface
contract HelloWorld is HelloWorldInterface {
    string private text;

    constructor() {
        text = "Hello World";
    }

    function helloWorld() public view override returns (string memory)  {
        return text;
    }

    // can use calldata instead of memory
    // cuz newText doesn't need to save into memory for setter
    function setText(string calldata newText) public override {
        text = newText;
    }
}

Replacing memory with calldata when stack is enough

data location : kinda low level thing... related w/ the cost
  - memory
  - storage
  - calldate: non-modifier, non-persistant

Relation between identifier and parameters and MethodID

Fallback and receive functions

contract HelloWorld is HelloWorldInterface {
  ...
  // it hits the fallback function because the attached function does not exist
  // when an error is occurred, just fallback
  fallback() external {
      text = "error";
  }
  ...
}

Definitions

Visibility

access point
 - public: inside + outside
 - private: inside
 - internal: inside
 - external: outside

State mutability
```
pure
view
payable
```
Modifiers
Virtual
Override

Error

Panic via assert and Error via require Properly functioning code should never create a Panic, not even on invalid external input. If this happens, then there is a bug in your contract which you should fix.

https://docs.soliditylang.org/en/latest/control-structures.html?highlight=require#error-handling-assert-require-revert-and-exceptions

contract HelloWorld is HelloWorldInterface {
    string private text;
    address public owner;

    constructor() {
        text = "Hello World";
        owner = msg.sender;
    }

    function helloWorld() public view override returns (string memory) {
        return text;
    }

    // function setText(string calldata newText) public override {
    //     require(msg.sender == owner, "Error");
    //     text = newText;
    // }

    function setText(string calldata newText) public override onlyOwner {
        text = newText;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        owner = newOwner;
    }

    modifier onlyOwner()
    {
        require (msg.sender == owner, "Caller is not the owner");
        _; // next function
    }
}