Data Location

Variables are stored in one of three places.

• storage - variable is a state variable (store on blockchain)
• memory - variable is in memory and it exists temporary during a function call
• calldata - special data location that contains function arguments

Difference between memory and calldata

calldata is like memory but not modifiable. calldata saves gas.

We cannot get the size of a mapping, and we can not iterate through the mapping to get all the values

Unless we internally keep track of all the keys in the mapping

Why we have to index events?

logging data on the blockchain ⇒ it IS a transaction and cannot be declared as view function

if you want to search for an event by the parameter that was logged, then we use the keyword indexed

Override

Calling Parent Constructors / Functions

• Parent contracts can be called directly, or using the keyword super.