as-if I'd ever let you.

Understanding the as-if rule in C++ interviews

This is an easy conceptual question about a foundational principle of the C++ standard. It appears in interviews at firms where candidates work with performance-critical code, because the as-if rule shapes what optimizations a compiler is permitted to perform and what guarantees a programmer can rely on.

The question tests whether you understand the contract between the C++ standard and compiler implementers. Specifically, it probes your grasp of what the standard permits compilers to do invisibly—and what it forbids—as long as the observable behavior of a program remains unchanged. This matters because it directly affects how you reason about memory ordering, side effects, and the semantics of seemingly equivalent code transformations.

• Compiler optimization boundaries
• Observable vs. unobservable program behavior
• The relationship between source code semantics and runtime behavior