Have printing function as class members in the header

src/engine/idTable/IdTable.h

@@ -751,6 +751,15 @@ class IdTableStatic
     *(static_cast<Base*>(this)) = std::move(b);
     return *this;
   }
+
+  friend std::ostream& operator<<(std::ostream& os,
+                                  const IdTableStatic& idTable) {
+    os << "{ ";
+    std::ranges::copy(
+        idTable, std::ostream_iterator<columnBasedIdTable::Row<Id>>(os, " "));
+    os << "}";
+    return os;
+  }
 };
 
 // This was previously implemented as an alias (`using IdTable =
@@ -766,15 +775,6 @@ class IdTable : public IdTableStatic<0> {
   IdTable(Base&& b) : Base(std::move(b)) {}
 };
 
-// ____________________________________________________________________________
-std::ostream& operator<<(std::ostream& os, const IdTable& idTable) {
-  os << "{ ";
-  std::ranges::copy(
-      idTable, std::ostream_iterator<columnBasedIdTable::Row<Id>>(os, " "));
-  os << "}";
-  return os;
-}
-
 /// A constant view into an IdTable that does not own its data
 template <int COLS>
 using IdTableView =

src/engine/idTable/IdTableRow.h

@@ -94,17 +94,16 @@ class Row {
     std::ranges::copy(*this, result.begin());
     return result;
   }
-};
 
-// ____________________________________________________________________________
-std::ostream& operator<<(std::ostream& os,
-                         const columnBasedIdTable::Row<Id>& idTableRow) {
-  os << "(";
-  for (size_t i = 0; i < idTableRow.numColumns(); ++i) {
-    os << idTableRow[i] << (i < idTableRow.numColumns() - 1 ? " " : ")");
+  template <std::enable_if_t<std::is_same_v<T, Id>, bool> = true>
+  friend std::ostream& operator<<(std::ostream& os, const Row& idTableRow) {
+    os << "(";
+    for (size_t i = 0; i < idTableRow.numColumns(); ++i) {
+      os << idTableRow[i] << (i < idTableRow.numColumns() - 1 ? " " : ")");
+    }
+    return os;
   }
-  return os;
-}
+};
 
 // The following two classes store a reference to a row in the underlying
 // column-based `Table`. This has to be its own class instead of `Row&` because