Visibility

Solidity provides four different types of visibility specifiers to help us control access to functions and variables.

Functions can be marked as public, private, internal, or external.
Variables can be marked as public, private, or internal.

1. public: Can be called by any contract or off-chain entity.
2. private: Can only be called from within the main contract.
3. internal: Can be called from within the main contract or a child contract.
4. external: Can be called from other contracts that do not inherit from the main contract, or any other off-chain entities.