From e29d9ae19e48dab84449f70d090c4ebc1dad3a78 Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Sun, 2 Sep 2018 20:40:49 +0200
Subject: [PATCH] TreeExplorer: better package this very specific code as
 subclass

while this is basically just code code cosmetics,
at least it marks this as a very distinct special case,
and keeps the API for the standard Filter layer clean.
---
 src/lib/iter-tree-explorer.hpp            | 33 +++++++++++++++++++----
 tests/library/iter-tree-explorer-test.cpp |  2 +-
 wiki/thinkPad.ichthyo.mm                  | 11 ++++++--
 3 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/src/lib/iter-tree-explorer.hpp b/src/lib/iter-tree-explorer.hpp
index da1d676b5..621f7b5be 100644
--- a/src/lib/iter-tree-explorer.hpp
+++ b/src/lib/iter-tree-explorer.hpp
@@ -863,6 +863,7 @@ namespace lib {
         using Res = typename _Traits::Res;
         static_assert(std::is_constructible<bool, Res>::value, "Functor must be a predicate");
         
+      protected:
         using FilterPredicate = typename _Traits::Functor;
         
         FilterPredicate predicate_;
@@ -911,7 +912,7 @@ namespace lib {
           }
         
         
-      private:
+      protected:
         SRC&
         srcIter()  const
           {
@@ -927,7 +928,17 @@ namespace lib {
             while (srcIter() and not predicate_(srcIter()))
               ++srcIter();
           }
-        
+      };
+    
+    
+    
+    template<class SRC, class FUN>
+    class MutableFilter
+      : public Filter<SRC,FUN>
+      {
+        using _Base = Filter<SRC,FUN>;
+      public:
+        using _Base::Filter;
         
         
       public: /* === API to Remould the Filter condition underway === */
@@ -957,13 +968,14 @@ namespace lib {
             using Res = typename _ChainTraits::Res;
             static_assert(std::is_constructible<bool, Res>::value, "Chained Functor must be a predicate");
             
+            using FilterPredicate = typename _Base::FilterPredicate;
             using ChainPredicate = typename _ChainTraits::Functor;
             
-            FilterPredicate& firstClause = this->predicate_;
+            FilterPredicate& firstClause = Filter<SRC,FUN>::predicate_;
             ChainPredicate chainClause{forward<COND> (additionalClause)};
             
-            predicate_ = FilterPredicate{buildCombinedClause (firstClause, chainClause)};
-            pullFilter();
+            _Base::predicate_ = FilterPredicate{buildCombinedClause (firstClause, chainClause)};
+            _Base::pullFilter();
           }
       };
     
@@ -1265,6 +1277,17 @@ namespace lib {
         }
       
       
+      template<class FUN>
+      auto
+      mutableFilter (FUN&& filterPredicate)
+        {
+          using ResCore = iter_explorer::MutableFilter<SRC, FUN>;
+          using ResIter = typename _DecoratorTraits<ResCore>::SrcIter;
+          
+          return TreeExplorer<ResIter> (ResCore {move(*this), forward<FUN>(filterPredicate)});
+        }
+      
+      
       /** _terminal builder_ to package the processing pipeline as IterSource.
        * Invoking this function moves the whole iterator compound, as assembled by the preceding
        * builder calls, into heap allocated memory and returns a [iterator front-end](\ref IterExploreSource).
diff --git a/tests/library/iter-tree-explorer-test.cpp b/tests/library/iter-tree-explorer-test.cpp
index 6f25ed072..ea4bda8b5 100644
--- a/tests/library/iter-tree-explorer-test.cpp
+++ b/tests/library/iter-tree-explorer-test.cpp
@@ -853,7 +853,7 @@ namespace test{
       verify_FilterChanges()
         {
           auto seq = treeExplore(CountDown{20})
-                       .filter([](uint){ return true; });
+                       .mutableFilter([](uint){ return true; });
           
           auto takeEve = [](uint i){ return i%2 == 0; };
           auto takeTrd = [](uint i){ return i%3 == 0; };
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 13adccc8c..38890073b 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -30977,7 +30977,8 @@
 </node>
 <node COLOR="#338800" CREATED="1535906261464" ID="ID_1343076549" MODIFIED="1535909947735" TEXT="Auswege">
 <icon BUILTIN="idea"/>
-<node CREATED="1535906265911" ID="ID_442265155" MODIFIED="1535906279633" TEXT="speziellen Filter-Layer nur hierf&#xfc;r">
+<node COLOR="#338800" CREATED="1535906265911" ID="ID_442265155" MODIFIED="1535913504313" TEXT="speziellen Filter-Layer nur hierf&#xfc;r">
+<icon BUILTIN="button_ok"/>
 <node CREATED="1535906327782" ID="ID_1903350743" MODIFIED="1535906334769" TEXT="letztlich nur Code-Kosmetik"/>
 <node CREATED="1535909106704" ID="ID_1756811057" MODIFIED="1535909115714" TEXT="w&#xfc;rde aber sehr speziellen Fall markieren"/>
 <node CREATED="1535909145091" ID="ID_23855152" MODIFIED="1535909185418">
@@ -31051,10 +31052,16 @@
 </node>
 </node>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535899873112" ID="ID_1460874987" MODIFIED="1535899882165" TEXT="Unit-Test (replizieren)">
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535899873112" ID="ID_1460874987" MODIFIED="1535913524436" TEXT="Unit-Test (replizieren)">
+<icon BUILTIN="pencil"/>
+<node COLOR="#338800" CREATED="1535913527837" ID="ID_1506533000" MODIFIED="1535913542932" TEXT="anlegen">
+<icon BUILTIN="button_ok"/>
+</node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535913531701" ID="ID_1093929821" MODIFIED="1535913541204" TEXT="andere F&#xe4;ll auch covern">
 <icon BUILTIN="flag-yellow"/>
 </node>
 </node>
+</node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1535899922873" ID="ID_1971708144" MODIFIED="1535899950863" TEXT="bestehende Aufrufe konsolidieren">
 <richcontent TYPE="NOTE"><html>
   <head>