Move get_charge_array to ElectrostaticsCollection (#1407)

* REF: Move `get_charge_array` to base class

* FIX: Fix type-checking

* DOC: Update release history

Author: mattwthompson

docs/releasehistory.md

@@ -29,6 +29,10 @@ Please note that all releases prior to a version 1.0.0 are considered pre-releas
 
 * #1396 Fixes charge ordering in Amber files
 
+### Miscellaneous improvements
+
+* #1407 `get_charge_array` is now defined on `ElectrostaticsCollection` and therefore accessible to subclasses `FoyerElectrostaticsHandler` and `BasicElectrostaticsCollection`. Previously, it was only defined on `SMIRNOFFElectrostaticsCollection`.
+
 ## 0.4.9 - 2025-11-06
 
 ### Behavior changes

openff/interchange/common/_nonbonded.py

@@ -119,6 +119,22 @@ def charges(
 
         return self._charges
 
+    def get_charge_array(self, include_virtual_sites: bool = False) -> Quantity:
+        """
+        Return a one-dimensional array-like of atomic charges, ordered topologically.
+
+        If virtual sites are present in the system, `NotImplementedError` is raised.
+        """
+        if include_virtual_sites:
+            raise NotImplementedError("Not yet implemented with virtual sites")
+
+        if VirtualSiteKey in {type(key) for key in self.key_map}:
+            raise NotImplementedError(
+                "Not yet implemented when virtual sites are present, even with `include_virtual_sites=False`.",
+            )
+
+        return Quantity.from_list([q for _, q in sorted(self.charges.items(), key=lambda x: x[0].atom_indices)])
+
     def _get_charges(
         self,
         include_virtual_sites: bool = False,

openff/interchange/interop/amber/export/_export.py

@@ -486,7 +486,7 @@ def to_prmtop(interchange: "Interchange", file_path: Path | str):
 
         prmtop.write("%FLAG CHARGE\n%FORMAT(5E16.8)\n")
         charges = (
-            interchange["Electrostatics"]  # type: ignore[attr-defined]
+            interchange["Electrostatics"]
             .get_charge_array()
             .m_as(
                 "elementary_charge",

openff/interchange/smirnoff/_nonbonded.py

@@ -343,22 +343,6 @@ def charges(
 
         return self._charges
 
-    def get_charge_array(self, include_virtual_sites: bool = False) -> Quantity:
-        """
-        Return a one-dimensional array-like of atomic charges, ordered topologically.
-
-        If virtual sites are present in the system, `NotImplementedError` is raised.
-        """
-        if include_virtual_sites:
-            raise NotImplementedError("Not yet implemented with virtual sites")
-
-        if VirtualSiteKey in {type(key) for key in self.key_map}:
-            raise NotImplementedError(
-                "Not yet implemented when virtual sites are present, even with `include_virtual_sites=False`.",
-            )
-
-        return Quantity.from_list([q for _, q in sorted(self.charges.items(), key=lambda x: x[0].atom_indices)])
-
     def _get_charges(
         self,
         include_virtual_sites: bool = True,