doc: Add switch on enum example to developer notes #17134

 586 | +    } // no default case, so the compiler can warn about missing cases
 587 | +    assert(false);
 588 | +}
 589 | +```
 590 | +
 591 | +*Rationale*: The comment documents skipping `default:` label, and it complies with `clang-format` rules. The assertion prevents firing of `-Wreturn-type` warning on some compilers.

MarcoFalke commented at 1:09 PM on October 14, 2019:

The warning is not wrong, though. While it is not undefined behavior to cast any int to an enum class type and pass it around (where it eventually will hit the assert), it seems the right thing to do for sanity.