What's statically wrong?

What this C++ static analysis question tests

This is a medium-difficulty C++23 code-reading problem that assesses your ability to spot compile-time errors in modern C++ syntax. Rather than asking you to write code, it challenges you to diagnose why a snippet fails to compile and articulate the underlying language rule being violated.

Questions like this are common in technical interviews because they reveal whether a candidate reads error messages carefully, understands the distinction between compile-time and runtime semantics, and has internalized the constraints of the language standard. The focus is on static correctness: knowing what the compiler requires before any code runs.

• C++23 language features and their constraints
• Compile-time vs. runtime semantics
• Reading and interpreting compiler diagnostics
• Type rules and declaration scoping