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Functions · easy

13. Modifiers

Reusable pre- and post-checks.

1 min read3 questionsup to 50 XPtopic 13/50

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A modifier wraps a function body, which runs where `_;` appears. They are ideal for access control and state guards, and keep the check in one auditable place.

solidity
modifier onlyOwner() {
    require(msg.sender == owner, "not owner");
    _;
}

function setRate(uint256 r) external onlyOwner { rate = r; }

Keep modifiers small: complex logic hidden in a modifier is easy to misread during review.

How to study this topic

  1. 1. Read the explanation once end to end, skipping the code.
  2. 2. Re-read the code snippets and say out loud what each line does.
  3. 3. Answer the quiz without scrolling back — that is the real check.
  4. 4. Read every explanation, even for the answers you got right.

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Check your understanding

  1. 1. What does `_;` mean in a modifier?

  2. 2. What are modifiers most used for?

  3. 3. Can several modifiers apply to one function?

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