TreeExplorer: refactor to make depth() reflect the logical expansion depth

...so sad.
The existing implementation was way more elegant,
just it discarded an exahusted parent element right while in expansion,
so effectively the child sequence took its place. Resolved that by
decomposing the iterNext() operation. And to keep it still readable,
I make the invariant of this class explicit and check it (which
caught yet another undsicovered bug. Yay!)

src/lib/iter-tree-explorer.hpp

@@ -545,11 +545,15 @@ namespace lib {
           {
             REQUIRE (this->checkPoint(), "attempt to expand an empty explorer");
             
-            ResIter expanded{ 0 < depth()? expandChildren_(*expansions_)
-                                         : expandChildren_(*this)};
-            iterNext();         // consume current head element
+            ResIter expanded{ hasChildren()? expandChildren_(*expansions_)
+                                           : expandChildren_(*this)};
+            incrementCurrent();   // consume current head element
             if (not isnil(expanded))
               expansions_.push (move(expanded));
+            else
+              dropExhaustedChildren();
+            
+            ENSURE (invariant());
           }
         
         /** diagnostics: current level of nested child expansion */
@@ -565,29 +569,56 @@ namespace lib {
         bool
         checkPoint()  const
           {
-            return 0 < depth()
-                or this->isValid();
+            ENSURE (invariant());
+            
+            return hasChildren()
+                or SRC::isValid();
           }
         
         typename SRC::reference
         yield()  const
           {
-            return 0 < depth()? **expansions_
-                              : **this;
+            return hasChildren()? **expansions_
+                                : **this;
           }
         
         void
         iterNext()
           {
-            if (0 < depth())
-              {
-                ++(*expansions_);
-                while (0 < depth() and not *expansions_)
-                  ++expansions_;
-              }
+            incrementCurrent();
+            dropExhaustedChildren();
+            ENSURE (invariant());
+          }
+        
+      private:
+        bool
+        invariant()  const
+          {
+            return not hasChildren()
+                or *expansions_;
+          }
+        
+        bool
+        hasChildren()  const
+          {
+            return 0 < depth();
+          }
+        
+        void
+        incrementCurrent()
+          {
+            if (hasChildren())
+              ++(*expansions_);
             else
               ++(*this);
           }
+        
+        void
+        dropExhaustedChildren()
+          {
+            while (not invariant())
+              ++expansions_;
+          }
       };
     
     

tests/library/iter-tree-explorer-test.cpp

@@ -961,6 +961,7 @@ namespace test{
               expandChildren()
                 {
                   src.expandChildren();
+                  protocol.resize (1+src.depth());
                 }
               
               bool

wiki/thinkPad.ichthyo.mm

@@ -5151,7 +5151,7 @@
 <linktarget COLOR="#585e9d" DESTINATION="ID_845080696" ENDARROW="Default" ENDINCLINATION="-101;761;" ID="Arrow_ID_402051988" SOURCE="ID_1359727169" STARTARROW="None" STARTINCLINATION="208;5;"/>
 <linktarget COLOR="#83dfc7" DESTINATION="ID_845080696" ENDARROW="Default" ENDINCLINATION="-1109;3887;" ID="Arrow_ID_1645152965" SOURCE="ID_30857289" STARTARROW="None" STARTINCLINATION="2051;-176;"/>
 <icon BUILTIN="button_ok"/>
-<node COLOR="#338800" CREATED="1511571446467" FOLDED="true" ID="ID_1778455053" MODIFIED="1513293453942" TEXT="expand-Operation">
+<node COLOR="#338800" CREATED="1511571446467" FOLDED="true" ID="ID_1778455053" MODIFIED="1513447893872" TEXT="expand-Operation">
 <icon BUILTIN="button_ok"/>
 <node COLOR="#338800" CREATED="1511227813712" ID="ID_1961708112" MODIFIED="1512927037831" TEXT="Fall-1">
 <icon BUILTIN="button_ok"/>
@@ -6330,6 +6330,41 @@
 </node>
 </node>
 </node>
+<node COLOR="#338800" CREATED="1513447925593" ID="ID_1239682661" MODIFIED="1513447946498" TEXT="expansion depth">
+<icon BUILTIN="button_ok"/>
+<node COLOR="#338800" CREATED="1513447947870" ID="ID_328146397" MODIFIED="1513448183232" TEXT="nach au&#xdf;en zug&#xe4;nglich machen">
+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1513447956069" ID="ID_1345517957" MODIFIED="1513447997648" TEXT="Problem: mu&#xdf; daf&#xfc;r korrekt sein">
+<icon BUILTIN="button_ok"/>
+<node CREATED="1513447967084" ID="ID_476332936" MODIFIED="1513447978718" TEXT="d.h. mu&#xdf; die logische Tiefe widerspiegeln"/>
+<node CREATED="1513447979450" ID="ID_224439756" MODIFIED="1513448250249" TEXT="...auch wenn der Vater bereits ersch&#xf6;pft ist">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      wir hatten bisher eine auto-Aufr&#228;um-Routine in iterNext(),
+    </p>
+    <p>
+      welche dazu f&#252;hrt, da&#223; ein ersch&#246;pfter Vater sofort wegger&#228;umt wird,
+    </p>
+    <p>
+      noch bevor wir dazu kommen, die Kinder zu pushen
+    </p>
+  </body>
+</html>
+</richcontent>
+</node>
+<node COLOR="#338800" CREATED="1513448002247" ID="ID_804459643" MODIFIED="1513448144858" TEXT="L&#xf6;sung">
+<linktarget COLOR="#63b5aa" DESTINATION="ID_804459643" ENDARROW="Default" ENDINCLINATION="456;372;" ID="Arrow_ID_1606709369" SOURCE="ID_1181955496" STARTARROW="None" STARTINCLINATION="1446;0;"/>
+<icon BUILTIN="idea"/>
+<node CREATED="1513448017406" ID="ID_753765398" MODIFIED="1513448275095" TEXT="iterNext aufspalten"/>
+<node CREATED="1513448019398" ID="ID_1143482463" MODIFIED="1513448026224" TEXT="Invariante explizit machen"/>
+</node>
+</node>
+</node>
 </node>
 <node COLOR="#338800" CREATED="1511837384749" ID="ID_274979743" MODIFIED="1513395614706" TEXT="asIterSource">
 <icon BUILTIN="button_ok"/>
@@ -7256,8 +7291,9 @@
 <arrowlink COLOR="#75c4c1" DESTINATION="ID_1752199055" ENDARROW="Default" ENDINCLINATION="653;643;" ID="Arrow_ID_1536391130" STARTARROW="None" STARTINCLINATION="1299;33;"/>
 <icon BUILTIN="button_ok"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1513401151507" ID="ID_1181955496" MODIFIED="1513401174705" TEXT="Protokoll aber immer noch nicht korrekt implementiert">
-<icon BUILTIN="flag-yellow"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1513401151507" ID="ID_1181955496" MODIFIED="1513448292560" TEXT="Protokoll aber immer noch nicht korrekt implementiert">
+<arrowlink COLOR="#63b5aa" DESTINATION="ID_804459643" ENDARROW="Default" ENDINCLINATION="456;372;" ID="Arrow_ID_1606709369" STARTARROW="None" STARTINCLINATION="1446;0;"/>
+<icon BUILTIN="pencil"/>
 <node CREATED="1513401162242" ID="ID_147162782" MODIFIED="1513401173005" TEXT="push am Ende"/>
 <node CREATED="1513401192358" ID="ID_91552039" MODIFIED="1513401294410" TEXT="Beispiel &quot;FAVSU&quot;">
 <richcontent TYPE="NOTE"><html>
@@ -7391,6 +7427,107 @@
 </node>
 <node CREATED="1513401185198" ID="ID_933999759" MODIFIED="1513401189850" TEXT="Z&#xe4;hler l&#xe4;uft weiter"/>
 </node>
+<node COLOR="#338800" CREATED="1513447822247" ID="ID_1725576262" MODIFIED="1513448159466" TEXT="jetzt scheint&apos;s zu funktionieren...">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      rLet(77943 &lt; 18446744073709551615) &#8594; R
+    </p>
+    <p>
+      |&#8623;| R ... 77943
+    </p>
+    <p>
+      rLet(77944 &lt; 18446744073709551615) &#8594; X
+    </p>
+    <p>
+      |!| expand 77944
+    </p>
+    <p>
+      rLet(0 &lt; 4) &#8594; U
+    </p>
+    <p>
+      rLet(77945 &lt; 18446744073709551615) &#8594; I
+    </p>
+    <p>
+      |.| U --&gt;&gt; 77944-0
+    </p>
+    <p>
+      |&#8623;| U ... 77944-0
+    </p>
+    <p>
+      rLet(1 &lt; 4) &#8594; X
+    </p>
+    <p>
+      |!| expand 77944-1
+    </p>
+    <p>
+      rLet(0 &lt; 4) &#8594; K
+    </p>
+    <p>
+      rLet(2 &lt; 4) &#8594; Z
+    </p>
+    <p>
+      |.| K --&gt;&gt; 77944-1-0
+    </p>
+    <p>
+      |!| expand 77944-1-0
+    </p>
+    <p>
+      rLet(0 &lt; 4) &#8594; V
+    </p>
+    <p>
+      rLet(1 &lt; 4) &#8594; Y
+    </p>
+    <p>
+      |.| V --&gt;&gt; 77944-1-0-0
+    </p>
+    <p>
+      |&#8623;| V ... 77944-1-0-0
+    </p>
+    <p>
+      rLet(1 &lt; 4) &#8594; I
+    </p>
+    <p>
+      |&#8623;| I ... 77944-1-0-1
+    </p>
+    <p>
+      rLet(2 &lt; 4) &#8594; I
+    </p>
+    <p>
+      |&#8623;| I ... 77944-1-0-2
+    </p>
+    <p>
+      rLet(3 &lt; 4) &#8594; Z
+    </p>
+    <p>
+      |!| expand 77944-1-0-3
+    </p>
+    <p>
+      rLet(0 &lt; 4) &#8594; Q
+    </p>
+    <p>
+      rLet(4 &lt; 4) &#8594; X
+    </p>
+    <p>
+      |.| Q --&gt;&gt; 77944-1-0-3-0
+    </p>
+    <p>
+      |&#8623;| Q ... 77944-1-0-3-0
+    </p>
+    <p>
+      rLet(1 &lt; 4) &#8594; M
+    </p>
+    <p>
+      Protocol of the search: 77944-1-0-3-1
+    </p>
+  </body>
+</html>
+</richcontent>
+<icon BUILTIN="button_ok"/>
+</node>
 </node>
 </node>
 </node>