core: New ot_transfer_out_value() macro

This makes out values considerably less typing.

src/libotutil/ot-gio-utils.c

@@ -186,11 +186,7 @@ ot_gio_splice_and_checksum (GOutputStream  *out,
     }
 
   ret = TRUE;
-  if (out_checksum)
-    {
-      *out_checksum = ret_checksum;
-      ret_checksum = NULL;
-    }
+  ot_transfer_out_value(out_checksum, ret_checksum);
  out:
   ot_clear_checksum (&ret_checksum);
   return ret;

src/libotutil/ot-unix-utils.c

@@ -22,7 +22,7 @@
 
 #include "config.h"
 
-#include "ot-unix-utils.h"
+#include "otutil.h"
 
 #include <gio/gio.h>
 #include <gio/gunixoutputstream.h>
@@ -67,8 +67,7 @@ ot_util_spawn_pager (GOutputStream  **out_stream,
       ret_stream = (GOutputStream*)g_unix_output_stream_new (stdin_fd, TRUE);
     }
 
-  *out_stream = ret_stream;
-  ret_stream = NULL;
+  ot_transfer_out_value(out_stream, ret_stream);
   ret = TRUE;
  out:
   g_clear_object (&ret_stream);

src/libotutil/ot-variant-utils.c

@@ -114,8 +114,7 @@ ot_util_variant_map (GFile *src,
   g_variant_ref_sink (ret_variant);
   
   ret = TRUE;
-  *out_variant = ret_variant;
-  ret_variant = NULL;
+  ot_transfer_out_value(out_variant, ret_variant);
  out:
   ot_clear_gvariant (&ret_variant);
   if (mfile)

src/libotutil/otutil.h

@@ -32,6 +32,14 @@
     }                                           \
   } G_STMT_END;
 
+#define ot_transfer_out_value(outp, srcp) G_STMT_START {   \
+  if (outp)                                                \
+    {                                                      \
+      *outp = srcp;                                        \
+      srcp = NULL;                                         \
+    }                                                      \
+  } G_STMT_END;
+
 #include <ot-gio-utils.h>
 #include <ot-glib-compat.h>
 #include <ot-opt-utils.h>