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ABI · medium

30. Function selectors and the ABI

How calldata identifies a function.

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A call's first four bytes are the selector: the first four bytes of `keccak256("transfer(address,uint256)")`. Arguments follow, ABI-encoded in 32-byte words.

solidity
bytes4 sel = bytes4(keccak256("stake(uint256)"));
abi.encodeWithSelector(sel, amount);

Use `abi.encodeCall(IERC20.transfer, (to, amt))` when you can: it type-checks the arguments against the real signature.

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  1. 1. How long is a function selector?

  2. 2. What is hashed to produce it?

  3. 3. Why prefer `abi.encodeCall`?

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