Functions: visibility, state mutability and modifiers — Solidity & Smart Contract Development

2. Functions: visibility, state mutability and modifiers

Basic★ Must knowLesson 2 of 11

Visibility	Callable from
`public`	Anywhere (internally and externally); public state vars get getters
`external`	Only from outside (other contracts/EOAs), or `this.f()`
`internal`	This contract and derived contracts (default for state variables)
`private`	Only this contract (still visible on-chain — not secret!)

Mutability	Meaning
(none)	Can read and modify state
`view`	Reads state, doesn't modify
`pure`	Neither reads nor modifies state
`payable`	Can receive Ether

solidity

function quote(uint256 qty) public view returns (uint256 price) { price = qty * unitPrice; }
function add(uint256 a, uint256 b) external pure returns (uint256) { return a + b; }

receive() external payable { }                       // plain Ether transfers (empty calldata)
fallback() external payable { }                      // unknown function selector (or Ether with data)

Modifiers wrap function logic (access control, state checks, reentrancy guard). Function overloading is allowed. Calls to view/pure functions from off-chain (eth_call) are free; when called inside a transaction they still cost gas.