Chapter 6

Functions and Modifiers

Functions are how users and other contracts interact with a smart contract. A good beginner habit is to read each function in terms of who can call it and what conditions must be true before it runs.

Function labels tell you where a function can be called from, while modifiers add reusable guardrails.

Visibility and modifiers

Keyword	Meaning	Typical use
public	Callable internally and externally	Simple getters or user actions
external	Callable from outside the contract	Functions mainly meant for users or other contracts
internal	Callable only inside this contract family	Shared helper logic
private	Callable only inside this contract	Very local helper behavior
modifier	Precondition wrapper like onlyOwner	Access control or sanity checks

Together they define both access and safety, which is why they appear in almost every Solidity codebase.

Visibility keywords answer a practical question: who gets to reach this code path? Modifiers answer the next question: what must already be true before the function body is allowed to continue?

This matters because many contract bugs are really access-control bugs. A mint function with the wrong visibility or a missing modifier can turn a private admin action into a public exploit.