View and Pure

View

The view keyword is a modifier used in Solidity to indicate that a function does not modify the state of the contract. View functions are able to access values from storage, but cannot modify them.

• It allows the function to call other functions which do not modify the state, while still disallowing other functions which do modify the state.

• The view keyword can also be used to make contracts more secure, as it ensures that data cannot be modified accidentally.

contract MyContract {    
    uint256 public myValue; 
    
    // view function
    function getMyValue() public view returns (uint256) {        
        return myValue;    
    }
}

• Since no state changes are made, the means that view functions can be called without incurring any gas costs.

Conditions for a statement to be considered as “modifying the state”:

1. State variables being written to.

2. Events being emitted.

3. Other contracts being created.

4. selfdestruct being used.

5. ETH being sent via calls.

6. Calling functions that are not marked view or pure.

7. Low-level calls being used.

8. Inline assembly containing certain opcodes being used

Events don't change the state of the contract where they are emitted but they change the state of the whole blockchain.

In simple terms, a log (emitting an event) will make a change in the Transaction Receipts Root that is recorded in the header of a block and a adding new block is considered a change in the state of the blockchain.

Pure

Pure function is one that does not interact with the blockchain in any way, including reading state of variables. It is self-encapsulated.

A pure function does not:

• Read or write to the blockchain

• Create or send a transaction

• Access any state variables

• Call any other functions

function convertWeiToEther(uint _amountInWei){
	return _amountInWei / 1 ether;
}

A pure function can ONLY call another pure function.