Function types

function (<parameter types>) {public|private|internal|external} 
[pure|view|payable] [(modifiers)] [returns (<return types>)]

A function declarations only impose scope and do nothing for security

Simply put:

public -> all can access

external -> only externally calls; cannot be accessed internally

internal -> only this contract and contracts deriving from it can access

private -> can only be accessed from within this contract

View

View functions do not modify the state, thus only being used for viewing the state. Therefore only can return data:

• List of 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

A View function can call on other View or Pure functions. Cannot call a writing f() -> else it would no longer be a read-only interaction.

Pure

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

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

A pure f() can ONLY call another pure f() -> anything else it would violate the rule and interact w/ SC.

a writing f() can call any.