Use exceptions for error handling only

Reason

To keep error handling separated from "ordinary code." C++ implementations tend to be optimized based on the assumption that exceptions are rare.

Example, don't

// don't: exception not used for error handling
int find_index(vector<string>& vec, const string& x)
{
    try {
        for (gsl::index i = 0; i < vec.size(); ++i)
            if (vec[i] == x) throw i;  // found x
    }
    catch (int i) {
        return i;
    }
    return -1;   // not found
}

This is more complicated and most likely runs much slower than the obvious alternative. There is nothing exceptional about finding a value in a vector.

Enforcement

Would need to be heuristic. Look for exception values "leaked" out of catch clauses.