When can't an object be converted to a reference

enh::eout << enh::setw(26);

error: no match for 'operator<<' in 'enh::eout << enh::setw(26)'

EnhSimOutput& operator<< (setw& p);

EnhSimOutput& operator<< (setw p);

enh::setw wValue(26);
enh::eout << wValue;

EnhSimOutput& operator<< (setw const& p);

int nNumber = 26;
enh::eout << enh::setw(nNumber);