chore: clean up OfType selector

ibis/selectors.py

@@ -128,6 +128,15 @@ def numeric() -> Selector:
     return of_type(dt.Numeric)
 
 
+class OfType(Selector):
+    predicate: Callable[[dt.DataType], bool]
+
+    def expand_names(self, table: ir.Table) -> frozenset[str]:
+        return frozenset(
+            name for name, typ in table.schema().items() if self.predicate(typ)
+        )
+
+
 @public
 def of_type(dtype: dt.DataType | str | type[dt.DataType]) -> Selector:
     """Select columns of type `dtype`.
@@ -186,17 +195,20 @@ def of_type(dtype: dt.DataType | str | type[dt.DataType]) -> Selector:
             "struct": dt.Struct,
             "temporal": dt.Temporal,
         }
-        if cls := abstract.get(dtype.lower()):
-            predicate = lambda col: isinstance(col.type(), cls)
+
+        if dtype_cls := abstract.get(dtype.lower()):
+            predicate = lambda typ, dtype_cls=dtype_cls: isinstance(typ, dtype_cls)
         else:
             dtype = dt.dtype(dtype)
-            predicate = lambda col: col.type() == dtype
+            predicate = lambda typ, dtype=dtype: typ == dtype
+
     elif inspect.isclass(dtype) and issubclass(dtype, dt.DataType):
-        predicate = lambda col: isinstance(col.type(), dtype)
+        predicate = lambda typ, dtype_cls=dtype: isinstance(typ, dtype_cls)
     else:
         dtype = dt.dtype(dtype)
-        predicate = lambda col: col.type() == dtype
-    return where(predicate)
+        predicate = lambda typ, dtype=dtype: typ == dtype
+
+    return OfType(predicate)
 
 
 class StartsWith(Selector):