ENH: Use cow for reindex_like (#50426)

Author: phofl

pandas/core/generic.py

@@ -4220,7 +4220,7 @@ def reindex_like(
         self: NDFrameT,
         other,
         method: Literal["backfill", "bfill", "pad", "ffill", "nearest"] | None = None,
-        copy: bool_t = True,
+        copy: bool_t | None = None,
         limit=None,
         tolerance=None,
     ) -> NDFrameT:

pandas/tests/copy_view/test_methods.py

@@ -387,6 +387,24 @@ def test_assign_drop_duplicates(using_copy_on_write, method):
     tm.assert_frame_equal(df, df_orig)
 
 
+def test_reindex_like(using_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": "a"})
+    other = DataFrame({"b": "a", "a": [1, 2]})
+
+    df_orig = df.copy()
+    df2 = df.reindex_like(other)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
 def test_reorder_levels(using_copy_on_write):
     index = MultiIndex.from_tuples(
         [(1, 1), (1, 2), (2, 1), (2, 2)], names=["one", "two"]