Message function selector

Why use this example

Use this pattern when the answer depends on transaction fields, block data, chain identity, payable value, or live RPC state. The entry isolates message function selector so its input, result, and state changes stay easy to compare.

Solidity to run

contract SelectorProbe {
  function capture(uint256) external pure returns (bytes4) {
    return msg.sig;
  }
}

SelectorProbe probe = new SelectorProbe()
probe.capture(42)
SelectorProbe.capture.selector

Official Solidity reference

Compare this focused investigation with the complete language definition in the Solidity documentation.

What to expect

The selector observed through msg.sig matches the capture function’s compile-time selector member.

Continue the investigation

Change a value, add another expression, or open Inspect after the run. Accepted entries remain available to the next entry, and the clean replay keeps the complete result reproducible.