Keep common and local names short, and keep uncommon and non-local names longer

Reason

Readability. Lowering the chance of clashes between unrelated non-local names.

Example

Conventional short, local names increase readability:

template<typename T>    // good
void print(ostream& os, const vector<T>& v)
{
    for (gsl::index i = 0; i < v.size(); ++i)
        os << v[i] << '\n';
}

An index is conventionally called i and there is no hint about the meaning of the vector in this generic function, so v is as good a name as any. Compare

template<typename Element_type>   // bad: verbose, hard to read
void print(ostream& target_stream, const vector<Element_type>& current_vector)
{
    for (gsl::index current_element_index = 0;
         current_element_index < current_vector.size();
         ++current_element_index
    )
    target_stream << current_vector[current_element_index] << '\n';
}

Yes, it is a caricature, but we have seen worse.

Example

Unconventional and short non-local names obscure code:

void use1(const string& s)
{
    // ...
    tt(s);   // bad: what is tt()?
    // ...
}

Better, give non-local entities readable names:

void use1(const string& s)
{
    // ...
    trim_tail(s);   // better
    // ...
}

Here, there is a chance that the reader knows what trim_tail means and that the reader can remember it after looking it up.

Example, bad

Argument names of large functions are de facto non-local and should be meaningful:

void complicated_algorithm(vector<Record>& vr, const vector<int>& vi, map<string, int>& out)
// read from events in vr (marking used Records) for the indices in
// vi placing (name, index) pairs into out
{
    // ... 500 lines of code using vr, vi, and out ...
}

We recommend keeping functions short, but that rule isn't universally adhered to and naming should reflect that.

Enforcement

Check length of local and non-local names. Also take function length into account.