Lesson 3 - Syntax and structure

Function definition

• Replacing memory with calldata when stack is enough
• Definitions
  • Visibility
  • State mutability
  • Modifiers
  • Virtual
  • Override

References

https://docs.soliditylang.org/en/latest/introduction-to-smart-contracts.html#storage-memory-and-the-stack

Code references

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;

contract HelloWorld {
    string private text;

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

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

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

Variable declaration and definition

• Elementary types
  • Booleans
  • Integers
  • Fixed
  • Address
  • Bytes
  • Strings
• State Variables
• Constants
• Data locations (again)
• Arrays
• Mappings

References

https://docs.soliditylang.org/en/latest/types.html

Exercises

• Extending new features

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
contract HelloWorld {
    string private text;

    constructor() {
        text = pureText();
    }

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

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

    function pureText() public pure returns (string memory) {
        return "Hello World";
    }

    function _isPure() internal view returns (bool _check) {
        _check = keccak256(bytes(text)) == keccak256(bytes(pureText()));
    }

    function isPure() public view returns (bool _returnValue) {
        _returnValue = _isPure();
    }

    function _restore() internal {
        text = pureText();
    }

    function restore() public returns (bool) {
        if (_isPure()) return false;
        _restore();
        return true;
    }
}

Common Solidity Global Variables

• Reserved words and global variables that a programmer should know
• Global variables about blockchain state
• Global variables about the transaction
• Global variables about the transaction message

References

https://docs.soliditylang.org/en/latest/units-and-global-variables.html

Assertion and Modifiers

• How errors are handled on solidity (briefly)
• Assertion
• Require statements
• Modifiers
• Where to use modifiers

References

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

https://docs.soliditylang.org/en/latest/structure-of-a-contract.html#function-modifiers

Homework

• Create Github Issues with your questions about this lesson
• Read the references