wip operator: more comments, going back to reading

Author: ym-pett

narwhals/_sql/expr.py

@@ -28,15 +28,17 @@
     from narwhals._sql.namespace import SQLNamespace
     from narwhals.typing import NumericLiteral, PythonLiteral, RankMethod, TemporalLiteral
 
-
-class SQLExpr(LazyExpr[SQLLazyFrameT, NativeExprT], Protocol[SQLLazyFrameT, NativeExprT]):
-    _call: EvalSeries[SQLLazyFrameT, NativeExprT]
+# am I right in thinking we need to pass NativeSQLExprT here, not NativeExprT? since NativeSQLExprT 
+# inherits from it, I can use that througout in the code and it will also have its parents functionality. 
+# though at the moment there are still problems with the class..
+class SQLExpr(LazyExpr[SQLLazyFrameT, NativeSQLExprT], Protocol[SQLLazyFrameT, NativeSQLExprT]):
+    _call: EvalSeries[SQLLazyFrameT, NativeSQLExprT]
     _evaluate_output_names: EvalNames[SQLLazyFrameT]
     _alias_output_names: AliasNames | None
     _version: Version
     _implementation: Implementation
     _metadata: ExprMetadata | None
-    _window_function: WindowFunction[SQLLazyFrameT, NativeExprT] | None
+    _window_function: WindowFunction[SQLLazyFrameT, NativeSQLExprT] | None
 
     def __init__(
         self,

narwhals/_sql/typing.py

@@ -35,8 +35,11 @@ def __mul__(self, value: Self) -> Self: ...
     # TODO: @mp, understand why these are here & if we need one for NativeSQLExprT;
     # seem to reflect number of different 'catgories' each of the parent class has
     # tbc! since NativeExpr only has Protocol, I don't think we need this for NativeSQLExpr
+    # NativeSQLExpr isn't accepting Any arguments :) I need to go back to the reading on 
+    # cov-, contra- & invariance
     SQLExprAny = SQLExpr[Any, Any]
     SQLLazyFrameAny = SQLLazyFrame[Any, Any, Any]
+    NativeSQLExprAny = NativeSQLExpr
 
 SQLExprT = TypeVar("SQLExprT", bound="SQLExprAny")
 SQLExprT_contra = TypeVar("SQLExprT_contra", bound="SQLExprAny", contravariant=True)