CH5-Data Storage and Scope

Storage location:

function setStoredData(uint256 newValue) public { storedData = newValue; // Modifies storage } }| | Memory | • Temporary storage that only exists during function execution • Used for function parameters, return values, and local variables • Much cheaper than storage in terms of gas costs • Data is erased after function completes |function memoryExample(uint[] memory myArray) public pure returns (uint) { uint[] memory localArray = new uint; localArray[0] = 1; return localArray[0]; }| | Calldata | •Read-only temporary storage for function parameters •Only available for external function parameters •cheapest for gas cost •immutable |function calldataExample(uint[] calldata myArray) external pure returns (uint) { return myArray[0]; // Read from calldata }` |

Variable scope:

CH6-Array & Struct

• Array:
• Struct:

CH7-Mapping

Mapping is used to store key-value pairs. They function similarly to hash tables in other programming languages

Syntax: mapping(keyType => valueType) visibility variableName;

Key Characteristics:

• Key Types: The key can be any built-in value type like uint, address, or bytes32. Complex types like arrays or structs are not allowed as keys.
• Value Types: The value can be of any type, including other mappings or structs.
• Default Values: All possible keys exist in a mapping and are mapped to the default value of the value type (e.g., 0 for uint).
• No Length: Mappings don't have a concept of length or size.
• Not Iterable: You cannot iterate over all elements in a mapping or get a list of all keys.

Note:

1. Storage: Mappings can only have the storage data location and are generally used for state variables.
2. Public Visibility: When declared public, Solidity automatically creates a getter function for the mapping.