From 544d71a4de8218cee20619caea58b1dc10e31321 Mon Sep 17 00:00:00 2001
From: Oleksiy <35204136+oleksiyskononenko@users.noreply.github.com>
Date: Fri, 28 Apr 2023 11:25:04 -0700
Subject: [PATCH] Minor refactoring of methods to get the underlying column
 type (#3458)

WIP for #1691
---
 src/core/column.h              |  1 -
 src/core/column/column_impl.cc |  3 +--
 src/core/column/column_impl.h  | 11 +++++++----
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/core/column.h b/src/core/column.h
index d8a399dec..1594fdfbb 100644
--- a/src/core/column.h
+++ b/src/core/column.h
@@ -119,7 +119,6 @@ class Column
     size_t nrows() const noexcept;
     size_t na_count() const;
     const dt::Type& type() const noexcept;
-    const dt::Type& data_type() const noexcept;
     dt::LType ltype() const noexcept;
     dt::SType stype() const noexcept;
 
diff --git a/src/core/column/column_impl.cc b/src/core/column/column_impl.cc
index 78e633696..bf65f1737 100644
--- a/src/core/column/column_impl.cc
+++ b/src/core/column/column_impl.cc
@@ -240,8 +240,7 @@ const Type& ColumnImpl::data_type() const {
 }
 
 SType ColumnImpl::data_stype() const {
-  return type_.is_categorical()? child(0).stype()
-                               : stype();
+  return data_type().stype();
 }
 
 
diff --git a/src/core/column/column_impl.h b/src/core/column/column_impl.h
index f5a50085c..a82f73ab8 100644
--- a/src/core/column/column_impl.h
+++ b/src/core/column/column_impl.h
@@ -95,10 +95,13 @@ class ColumnImpl
     size_t nrows() const noexcept { return nrows_; }
     SType stype() const { return type_.stype(); }
     const Type& type() const { return type_; }
-    const Type& data_type() const {
-      return type_.is_categorical()? child(0).type()
-                                   : type_;
-    }
+
+    // For categorical columns these methods will return the stype/type
+    // of the data the column is backed up with. For all the other column types,
+    // these methods are equivalent to `stype()`/`type()`.
+    SType data_stype() const;
+    const Type& data_type() const;
+
     virtual bool is_virtual() const noexcept = 0;
     virtual bool computationally_expensive() const { return false; }
     virtual size_t memory_footprint() const noexcept = 0;