I see no good reason to make the arrow interface a separate lib. Let's just make it optionally compiled in the main target.

CMakeLists.txt

@@ -32,8 +32,7 @@ if(TESTS)
 endif()
 
 if(ARROW)
-    add_subdirectory(arrow/xlntarrow)
+    add_subdirectory(xlntpyarrow)
-    add_subdirectory(arrow/xlntpyarrow)
 endif()
 
 add_subdirectory(source)

arrow/xlntarrow/CMakeLists.txt

@@ -1,30 +0,0 @@
-cmake_minimum_required(VERSION 3.2)
-project(xlntarrow)
-
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
-
-option(CONDA_ROOT "Path to Conda directory." "")
-if(NOT CONDA_ROOT)
-    message(FATAL_ERROR "Missing Conda root directory option (-D CONDA_ROOT).")
-endif()
-
-set(XLNT_ARROW
-    ${CMAKE_CURRENT_SOURCE_DIR}/xlntarrow.hpp
-    ${CMAKE_CURRENT_SOURCE_DIR}/xlntarrow.cpp)
-
-link_directories(${CONDA_ROOT}/lib)
-
-if(NOT STATIC)
-	add_library(xlntarrow SHARED ${XLNT_ARROW})
-	target_compile_definitions(xlntarrow PRIVATE XLNT_EXPORT=1)
-else()
-	add_library(xlntarrow STATIC ${XLNT_ARROW})
-endif()
-
-target_link_libraries(xlntarrow PRIVATE xlnt)
-target_link_libraries(xlntarrow PRIVATE arrow)
-
-target_include_directories(xlntarrow PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
-target_include_directories(xlntarrow PRIVATE ${CONDA_ROOT}/include)
-

include/xlnt/workbook/streaming_workbook_writer.hpp

@@ -25,6 +25,8 @@
 
 #include <cstddef>
 #include <iterator>
+#include <string>
+#include <vector>
 
 #include <xlnt/xlnt_config.hpp>
 
@@ -34,6 +36,10 @@ class serializer;
 
 namespace xlnt {
 
+class cell;
+class cell_reference;
+class worksheet;
+
 namespace detail {
 class xlsx_producer;
 } // namespace detail

source/CMakeLists.txt

@@ -118,6 +118,16 @@ if(NOT BIN_DEST_DIR)
     set(BIN_DEST_DIR ${CMAKE_INSTALL_PREFIX}/bin)
 endif()
 
+if(ARROW)
+	option(CONDA_ROOT "Path to Conda directory." "")
+
+	if(NOT CONDA_ROOT)
+	    message(FATAL_ERROR "Missing Conda root directory option (-D CONDA_ROOT).")
+	endif()
+
+	link_directories(${CONDA_ROOT}/lib)
+endif()
+
 if(NOT STATIC)
     add_library(xlnt SHARED ${XLNT_HEADERS} ${XLNT_SOURCES} $<TARGET_OBJECTS:libstudxml>)
     target_compile_definitions(xlnt PRIVATE XLNT_SHARED=1)
@@ -155,6 +165,11 @@ target_include_directories(xlnt PUBLIC ${XLNT_INCLUDE_DIR})
 target_include_directories(xlnt PRIVATE ${XLNT_SOURCE_DIR})
 target_include_directories(xlnt PRIVATE ${XLNT_SOURCE_DIR}/../third-party/libstudxml)
 
+if(ARROW)
+	target_link_libraries(xlnt PRIVATE arrow)
+	target_include_directories(xlnt PRIVATE ${CONDA_ROOT}/include)
+endif()
+
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.0.0")
     target_compile_definitions(xlnt PRIVATE UTFCPP=1)
     target_include_directories(xlnt PRIVATE ${XLNT_SOURCE_DIR}/../third-party/utfcpp)

source/utils/xlntarrow.cpp

@@ -1,10 +1,14 @@
-#include <xlnt/xlnt.hpp>
+#include <xlnt/cell/cell.hpp>
-#include <xlntarrow.hpp>
+#include <xlnt/cell/cell_reference.hpp>
+#include <xlnt/workbook/streaming_workbook_reader.hpp>
+#include <xlnt/workbook/streaming_workbook_writer.hpp>
+#include <xlnt/worksheet/worksheet.hpp>
+#include <xlnt/utils/xlntarrow.hpp>
 
 namespace xlnt {
 namespace arrow {
 
-void xlsx2arrow(std::istream &s, ::arrow::Table &table)
+void XLNT_API xlsx2arrow(std::istream &s, ::arrow::Table &table)
 {
     xlnt::streaming_workbook_reader reader;
     reader.open(s);
@@ -30,7 +34,7 @@ void xlsx2arrow(std::istream &s, ::arrow::Table &table)
     reader.end_worksheet();
 }
 
-void arrow2xlsx(const ::arrow::Table &table, std::ostream &s)
+void XLNT_API arrow2xlsx(const ::arrow::Table &table, std::ostream &s)
 {
   xlnt::streaming_workbook_writer writer;
   writer.open(s);

xlntpyarrow/CMakeLists.txt

@@ -10,4 +10,5 @@ configure_file("${CMAKE_CURRENT_SOURCE_DIR}/setup.py.cmake"
 
 add_custom_target(xlntpyarrow ALL
     COMMAND python setup.py build
-    DEPENDS xlntarrow)
+    DEPENDS xlntarrow
+	SOURCES xlntpyarrow.cpp setup.py.cmake)

xlntpyarrow/setup.py.cmake

@@ -16,8 +16,7 @@ conda_root = '${CONDA_ROOT}'
 
 include_dirs = [
     os.path.join(project_root, 'include'),
-    os.path.join(project_root, 'arrow/xlntarrow'),
+    os.path.join(project_root, 'xlntpyarrow'),
-    os.path.join(project_root, 'arrow/xlntpyarrow'),
     os.path.join(conda_root, 'include')
 ]
 
@@ -27,7 +26,6 @@ if os.name == 'nt':
     subdirectory = '/Release'
 
 library_dirs = [
-    os.path.join(project_root, 'build/arrow/xlntarrow' + subdirectory),
     os.path.join(project_root, 'build/source' + subdirectory),
     os.path.join(conda_root, 'lib')
 ]
@@ -41,7 +39,6 @@ xlntpyarrow_extension = Extension(
     include_dirs = include_dirs,
     libraries = [
         'arrow',
-        'xlntarrow',
         'xlnt'
     ],
     library_dirs = library_dirs,

xlntpyarrow/xlntpyarrow.cpp

@@ -1,7 +1,7 @@
 #include <iostream>
 #include <memory>
 #include <vector>
-#include <xlntarrow.hpp>
+#include <xlnt/utils/xlntarrow.hpp>
 #include <python_streambuf.hpp>
 #include <Python.h>