Macro op 

op!() { /* proc-macro */ }

preprocessor::op!(...) — Expression-level macro for compile-time evaluation.

Parses the input expression, evaluates all evaluable sub-expressions at compile time, and replaces them with literal results. Non-evaluable parts (free variables, etc.) are passed through unchanged.

Example

let result = preprocessor::op!(1 + 2 * 3);  // → let result = 7;
let x = preprocessor::op!(a + 1);           // → let x = a + 1; (passthrough)