Question

This is a language design question:

Do you think unreachable code (in programming languages in general) should raise a warning (i.e. “report problem and compile anyway”) or an error (“refuse to compile”)?

Personally I strongly feel it should be an error: if the programmer writes a piece of code, it should always be with the intention of actually running it in some scenario. But the C# compiler for example seems to disagree with this and merely reports a warning.

Note: I realize good dead code detection is a very difficult problem, but that is not the focus of this question.

Here are some examples of pieces of code where some statements are clearly unreachable:

return;
foo();

—

throw new Exception();
foo();

—

if (...) {
  return;
} else {
  throw new Exception();
}
foo();

Answer 1

Generally speaking it should be an error.

One exception comes to my mind however:

if (false) {
  doStuffThatITemporarilyDisabled();
}

Some developers might complain if your compiler denies compilation for code like that.