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Types · easy

3. Variables and visibility

State, local and global variables, and who can read them.

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State variables live in storage and persist between calls. Local variables live only for the duration of a call. Global variables such as `msg.sender`, `msg.value` and `block.timestamp` describe the current transaction and block.

Visibility on state variables controls Solidity-level access: `public` (auto-generates a getter), `internal` (this contract and children, the default) and `private` (this contract only).

solidity
uint256 public totalStaked;   // getter generated
uint256 internal cachedRate;
address private _admin;

`private` is not secrecy: all storage is readable off chain. Never store secrets in a contract.

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Check your understanding

  1. 1. What does `public` add to a state variable?

  2. 2. Can anyone read a `private` variable's value?

  3. 3. Which is the default visibility for state variables?

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