From 9460f79039324434b4774063c3c46d2696bccedc Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Sat, 18 Nov 2017 19:28:57 +0100
Subject: [PATCH] WIP: draft how to figure out the kind of iterator

...but does not work as intended:
 * just forming an IterStateWrapper does not trigger SFINAE cleanly in all cases
 * IterStateWrapper can be formed, even when some of the extension points are missing;
   this will be uncovered only later, when actually using one of the operations

but beyond that, the basic type selection logic can work this way
---
 src/lib/iter-tree-explorer.hpp | 45 ++++++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/src/lib/iter-tree-explorer.hpp b/src/lib/iter-tree-explorer.hpp
index f52f8ae07..f8b6c4dff 100644
--- a/src/lib/iter-tree-explorer.hpp
+++ b/src/lib/iter-tree-explorer.hpp
@@ -72,7 +72,8 @@
 
 
 #include "lib/error.hpp"
-#include "lib/meta/function.hpp"
+#include "lib/meta/trait.hpp"
+//#include "lib/meta/function.hpp"
 #include "lib/iter-adapter.hpp"
 #include "lib/iter-stack.hpp"
 #include "lib/meta/trait.hpp" ////////////////TODO
@@ -157,10 +158,48 @@ namespace lib {
   }//(End) namespace iter_explorer : predefined policies and configurations
   namespace {
     
+    using meta::enable_if;
+    using std::__and_;
+    using std::__not_;
+    using std::is_constructible;
+    using meta::can_IterForEach;
+    using meta::can_STL_ForEach;
+    
+    template<class SRC>
+    struct is_StateCore
+      : is_constructible<lib::IterStateWrapper<typename SRC::value_type, SRC>, SRC>
+      { };
+    
+    template<class SRC>
+    struct shall_wrap_STL_Iter
+      : __and_<can_STL_ForEach<SRC>
+              ,__not_<can_IterForEach<SRC>>
+              >
+      { };
+    
+    
     template<class SRC, typename SEL=void>
     struct _TreeExplorerTraits
       {
-        
+        static_assert (!sizeof(SRC), "Can not build TreeExplorer: Unable to figure out how to iterate the given SRC type.");
+      };
+    
+    template<class SRC>
+    struct _TreeExplorerTraits<SRC,   enable_if<is_StateCore<SRC>>>
+      {
+        static_assert (!sizeof(SRC), "PLING: StateCore");
+      };
+    
+    template<class SRC>
+    struct _TreeExplorerTraits<SRC,   enable_if<can_IterForEach<SRC>>>
+      {
+        static_assert (!sizeof(SRC), "PLING: Lumi Iter");
+      };
+    
+    template<class SRC>
+    struct _TreeExplorerTraits<SRC,   enable_if<shall_wrap_STL_Iter<SRC>>>
+      {
+        static_assert (!sizeof(SRC), "PLING: STL Iter");
       };
     
   }//(End) TreeExplorer traits
@@ -174,6 +213,8 @@ namespace lib {
   inline auto
   treeExplore (IT&& srcSeq)
   {
+    using SrcIter = typename _TreeExplorerTraits<IT>::SrcIter;
+    
     return TreeExplorer<SrcIter> {std::forward<IT>(srcSeq)};
   }