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Functions · easy

4. Functions and visibility

public, external, internal, private and how calls arrive.

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A function declares parameters, visibility, optional mutability and return types.

`external` functions can only be called from outside (or via `this.f()`); `public` works both ways; `internal` is callable by this contract and inheritors; `private` only inside this contract.

solidity
function stake(uint256 amount) external { }
function _credit(address user, uint256 amount) internal { }
function rate() public view returns (uint256) { return 5; }

Prefer `external` for the user-facing surface and `internal` helpers prefixed with an underscore — it keeps the ABI small and the intent obvious.

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Check your understanding

  1. 1. Which visibility means 'callable only from outside the contract'?

  2. 2. Which visibility do inheriting contracts get access to?

  3. 3. What is a common convention for internal helpers?

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