[refactor] SWIG - Split pointer manipulation to individual .i file (#3538)

* [refactor] SWIG - Split pointer manipulation to individual .i file

* Update module docstring

* space

swig/lightgbmlib.i

@@ -279,102 +279,6 @@
   }
 %}
 
-%pointer_functions(int, intp)
-%pointer_functions(long, longp)
-%pointer_functions(double, doublep)
-%pointer_functions(float, floatp)
-%pointer_functions(int64_t, int64_tp)
-%pointer_functions(int32_t, int32_tp)
-
-%pointer_cast(int64_t *, long *, int64_t_to_long_ptr)
-%pointer_cast(int64_t *, double *, int64_t_to_double_ptr)
-%pointer_cast(int32_t *, int *, int32_t_to_int_ptr)
-%pointer_cast(long *, int64_t *, long_to_int64_t_ptr)
-%pointer_cast(double *, int64_t *, double_to_int64_t_ptr)
-%pointer_cast(int *, int32_t *, int_to_int32_t_ptr)
-
-%pointer_cast(double *, void *, double_to_voidp_ptr)
-%pointer_cast(float *, void *, float_to_voidp_ptr)
-%pointer_cast(int *, void *, int_to_voidp_ptr)
-%pointer_cast(int32_t *, void *, int32_t_to_voidp_ptr)
-%pointer_cast(int64_t *, void *, int64_t_to_voidp_ptr)
-
-/* Custom pointer manipulation template */
-%define %pointer_manipulation(TYPE, NAME)
-%{
-  static TYPE *new_##NAME() { %}
-  %{  TYPE* NAME = new TYPE; return NAME; %}
-  %{}
-
-  static void delete_##NAME(TYPE *self) { %}
-  %{  if (self) delete self; %}
-  %{}
-  %}
-
-TYPE *new_##NAME();
-void  delete_##NAME(TYPE *self);
-
-%enddef
-
-%define %pointer_dereference(TYPE, NAME)
-%{
-  static TYPE NAME ##_value(TYPE *self) {
-    TYPE NAME = *self;
-    return NAME;
-  }
-%}
-
-TYPE NAME##_value(TYPE *self);
-
-%enddef
-
-%define %pointer_handle(TYPE, NAME)
-%{
-  static TYPE* NAME ##_handle() { %}
-  %{ TYPE* NAME = new TYPE; *NAME = (TYPE)operator new(sizeof(int*)); return NAME; %}
-  %{}
-%}
-
-TYPE *NAME##_handle();
-
-%enddef
-
-%define %long_array_functions(TYPE,NAME)
-%{
-  static TYPE *new_##NAME(int64_t nelements) { %}
-  %{  return new TYPE[nelements](); %}
-  %{}
-
-  static void delete_##NAME(TYPE *ary) { %}
-  %{  delete [] ary; %}
-  %{}
-
-  static TYPE NAME##_getitem(TYPE *ary, int64_t index) {
-    return ary[index];
-  }
-  static void NAME##_setitem(TYPE *ary, int64_t index, TYPE value) {
-    ary[index] = value;
-  }
-  %}
-
-TYPE *new_##NAME(int64_t nelements);
-void delete_##NAME(TYPE *ary);
-TYPE NAME##_getitem(TYPE *ary, int64_t index);
-void NAME##_setitem(TYPE *ary, int64_t index, TYPE value);
-
-%enddef
-
-%long_array_functions(double, doubleArray)
-%long_array_functions(float, floatArray)
-%long_array_functions(int, intArray)
-%long_array_functions(long, longArray)
-
-%pointer_manipulation(void*, voidpp)
-
-/* Allow dereferencing of void** to void* */
-%pointer_dereference(void*, voidpp)
-
-/* Allow retrieving handle to void** */
-%pointer_handle(void*, voidpp)
 
+%include "pointer_manipulation.i"
 %include "StringArray_API_extensions.i"

swig/pointer_manipulation.i

@@ -0,0 +1,114 @@
+/*!
+ * Copyright (c) 2018 Microsoft Corporation. All rights reserved.
+ * Licensed under the MIT License. See LICENSE file in the project root for license information.
+ */
+/*!
+ * This SWIG interface extension provides support to
+ * the pointer manipulation methods present in the standard
+ * SWIG wrappers, but with support for larger arrays.
+ * 
+ * SWIG provides this in https://github.com/swig/swig/blob/master/Lib/carrays.i
+ * but the standard methods only provide arrays with up to
+ * max(int32_t) elements.
+ * 
+ * The `long_array_functions` wrappers extend this
+ * to arrays of size max(int64_t) instead of max(int32_t).
+ */
+
+%pointer_functions(int, intp)
+%pointer_functions(long, longp)
+%pointer_functions(double, doublep)
+%pointer_functions(float, floatp)
+%pointer_functions(int64_t, int64_tp)
+%pointer_functions(int32_t, int32_tp)
+
+%pointer_cast(int64_t *, long *, int64_t_to_long_ptr)
+%pointer_cast(int64_t *, double *, int64_t_to_double_ptr)
+%pointer_cast(int32_t *, int *, int32_t_to_int_ptr)
+%pointer_cast(long *, int64_t *, long_to_int64_t_ptr)
+%pointer_cast(double *, int64_t *, double_to_int64_t_ptr)
+%pointer_cast(int *, int32_t *, int_to_int32_t_ptr)
+
+%pointer_cast(double *, void *, double_to_voidp_ptr)
+%pointer_cast(float *, void *, float_to_voidp_ptr)
+%pointer_cast(int *, void *, int_to_voidp_ptr)
+%pointer_cast(int32_t *, void *, int32_t_to_voidp_ptr)
+%pointer_cast(int64_t *, void *, int64_t_to_voidp_ptr)
+
+/* Custom pointer manipulation template */
+%define %pointer_manipulation(TYPE, NAME)
+%{
+  static TYPE *new_##NAME() { %}
+  %{  TYPE* NAME = new TYPE; return NAME; %}
+  %{}
+
+  static void delete_##NAME(TYPE *self) { %}
+  %{  if (self) delete self; %}
+  %{}
+  %}
+
+TYPE *new_##NAME();
+void  delete_##NAME(TYPE *self);
+
+%enddef
+
+%define %pointer_dereference(TYPE, NAME)
+%{
+  static TYPE NAME ##_value(TYPE *self) {
+    TYPE NAME = *self;
+    return NAME;
+  }
+%}
+
+TYPE NAME##_value(TYPE *self);
+
+%enddef
+
+%define %pointer_handle(TYPE, NAME)
+%{
+  static TYPE* NAME ##_handle() { %}
+  %{ TYPE* NAME = new TYPE; *NAME = (TYPE)operator new(sizeof(int*)); return NAME; %}
+  %{}
+%}
+
+TYPE *NAME##_handle();
+
+%enddef
+
+%define %long_array_functions(TYPE,NAME)
+%{
+  static TYPE *new_##NAME(int64_t nelements) { %}
+  %{  return new TYPE[nelements](); %}
+  %{}
+
+  static void delete_##NAME(TYPE *ary) { %}
+  %{  delete [] ary; %}
+  %{}
+
+  static TYPE NAME##_getitem(TYPE *ary, int64_t index) {
+    return ary[index];
+  }
+  static void NAME##_setitem(TYPE *ary, int64_t index, TYPE value) {
+    ary[index] = value;
+  }
+  %}
+
+TYPE *new_##NAME(int64_t nelements);
+void delete_##NAME(TYPE *ary);
+TYPE NAME##_getitem(TYPE *ary, int64_t index);
+void NAME##_setitem(TYPE *ary, int64_t index, TYPE value);
+
+%enddef
+
+%long_array_functions(double, doubleArray)
+%long_array_functions(float, floatArray)
+%long_array_functions(int, intArray)
+%long_array_functions(long, longArray)
+
+%pointer_manipulation(void*, voidpp)
+
+/* Allow dereferencing of void** to void* */
+%pointer_dereference(void*, voidpp)
+
+/* Allow retrieving handle to void** */
+%pointer_handle(void*, voidpp)