From 27b36f067901422ab4b9f72fa407619aef9a385e Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Tue, 28 May 2024 18:07:08 +0200
Subject: [PATCH] Library: implement access to storage and subscript

...not sure if this approach works out OK,
since we can not make a safe downcast to a size known at runtime
---
 src/lib/several-builder.hpp |  5 ++++-
 src/lib/several.hpp         | 44 +++++++++++++++++++++++++++++--------
 wiki/thinkPad.ichthyo.mm    | 25 ++++++++++++++++++++-
 3 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/src/lib/several-builder.hpp b/src/lib/several-builder.hpp
index 96f6f95dd..dc96d2c86 100644
--- a/src/lib/several-builder.hpp
+++ b/src/lib/several-builder.hpp
@@ -46,8 +46,11 @@
 #include "lib/several.hpp"
 #include "include/logging.h"
 
+#include <utility>
 #include <vector>
+
 using std::vector;
+using std::move;
 
 
 
@@ -75,7 +78,7 @@ namespace lib {
       Several<I>
       build()
         {
-          UNIMPLEMENTED ("materialise into Several-Container");
+          return move (*this);
         }
     };
   
diff --git a/src/lib/several.hpp b/src/lib/several.hpp
index 743c55a62..364a032e9 100644
--- a/src/lib/several.hpp
+++ b/src/lib/several.hpp
@@ -57,6 +57,9 @@ namespace lib {
         
         Manager manager;
         size_t spread;
+        
+        template<class I>
+        auto access();
       };
     
     template<class I, size_t bytes>
@@ -65,8 +68,27 @@ namespace lib {
       {
         alignas(I)
           std::byte storage[bytes];
+        
+        I&
+        subscript (size_t idx)
+          {
+            std::byte* elm = storage;
+            size_t off = idx * spread;
+            elm += off;
+            return * std::launder (reinterpret_cast<I*> (elm));
+          }
       };
     
+    
+    /** @internal perform an unsafe down-cast to access the storage area */
+    template<class I>
+    auto
+    Bucket::access()
+    {
+      using Storage = ArrayBucket<I, sizeof(I)>;
+      return static_cast<Storage&> (*this);
+    }
+    
   }//(End)implementation details
   
   
@@ -80,7 +102,7 @@ namespace lib {
    */
   template<class I>
   class Several
-    : util::MoveOnly
+    : util::MoveAssign
     {
     protected:
       size_t  size_{0};
@@ -91,20 +113,24 @@ namespace lib {
       size_t
       size()  const
         {
-          UNIMPLEMENTED ("determine storage size");
+          return size_;
+        }
+      
+      bool
+      empty()  const
+        {
+          return not (size_ and data_);
         }
       
       I&
-      operator[] (size_t i)
+      operator[] (size_t idx)
         {
-          UNIMPLEMENTED ("subscript");
+          REQUIRE (data_);
+          return data_->access<I>().subscript (idx);
         }
       
-      I&
-      back()
-        {
-          UNIMPLEMENTED ("storage access");
-        }
+      I& front() { return operator[] (size_-1); }
+      I& back()  { return operator[] (0);       }
       
       using iterator = I*;
       using const_iterator = I const*;
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 5c1656df8..5426aa3f5 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -81846,15 +81846,38 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716907249314" ID="ID_1711986050" MODIFIED="1716907418033" TEXT="Bucket">
 <node CREATED="1716907252393" ID="ID_198747165" MODIFIED="1716907259884" TEXT="der Descriptor"/>
 <node CREATED="1716907260424" ID="ID_1362772717" MODIFIED="1716907268555" TEXT="liegt am Anfang der Element-Storage"/>
+<node CREATED="1716912140198" ID="ID_9984568" MODIFIED="1716912197368" TEXT="erm&#xf6;glicht beliebigen Down-cast auf gegebene Storage-Gr&#xf6;&#xdf;e">
+<linktarget COLOR="#a9b4c1" DESTINATION="ID_9984568" ENDARROW="Default" ENDINCLINATION="97;4;" ID="Arrow_ID_396222637" SOURCE="ID_581123494" STARTARROW="None" STARTINCLINATION="0;-15;"/>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716906944780" ID="ID_1643896091" MODIFIED="1716907418033" TEXT="ArrayBucket&lt;I,bytes&gt;">
 <node CREATED="1716907277198" ID="ID_104268426" MODIFIED="1716907281769" TEXT="Subklasse von Bucket"/>
 <node CREATED="1716907312241" ID="ID_835337350" MODIFIED="1716907333394" TEXT="umspannt das Storage-Array"/>
-<node CREATED="1716907356091" ID="ID_1876919425" MODIFIED="1716907403909" TEXT="enth&#xe4;lt den subscript-Code"/>
+<node COLOR="#338800" CREATED="1716907356091" ID="ID_1876919425" MODIFIED="1716912200686" TEXT="enth&#xe4;lt den subscript-Code">
+<icon BUILTIN="button_ok"/>
+<node BACKGROUND_COLOR="#f8f1cb" COLOR="#a50125" CREATED="1716912163674" ID="ID_581123494" MODIFIED="1716912308218" TEXT="mu&#xdf; hier einen offenen Downcast machen">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      ...weil ich den Zieltyp zum Cast nicht dynamisch konstruieren kann
+    </p>
+  </body>
+</html>
+</richcontent>
+<arrowlink DESTINATION="ID_9984568" ENDARROW="Default" ENDINCLINATION="97;4;" ID="Arrow_ID_396222637" STARTARROW="None" STARTINCLINATION="0;-15;"/>
+<icon BUILTIN="messagebox_warning"/>
 </node>
 </node>
 </node>
 </node>
+<node CREATED="1716909012702" ID="ID_1876994172" MODIFIED="1716909016713" TEXT="const-correctness">
+<node CREATED="1716909019405" ID="ID_1406909807" MODIFIED="1716909042294" TEXT="ein const Several&lt;X&gt; ist ein Several&lt;const X&gt;"/>
+</node>
+</node>
+</node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1715625082614" ID="ID_1575150785" MODIFIED="1715625089779" TEXT="SeveralBuilder_test">
 <icon BUILTIN="flag-yellow"/>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1716857382440" ID="ID_46730448" MODIFIED="1716857402102" TEXT="simpleUsage">