From 551670052314867b7db66ad69946567914c6fb57 Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Sun, 18 Mar 2018 02:11:46 +0100
Subject: [PATCH] DI: draft configuration for using a service implementation
 created elsewhere

---
 research/try.cpp         | 80 +++++++++++++++++++++++++++++++++++++++-
 wiki/thinkPad.ichthyo.mm | 21 ++++++++---
 2 files changed, 93 insertions(+), 8 deletions(-)

diff --git a/research/try.cpp b/research/try.cpp
index 04483dc2c..2d46eb391 100644
--- a/research/try.cpp
+++ b/research/try.cpp
@@ -200,6 +200,24 @@ class DependInject
         Depend<SRV>::factory = Depend<SRV>::disabledFactory;
       }
     
+    static void
+    activateServiceAccess (SRV& newInstance)
+      {
+        ClassLock<SRV> guard;
+        if (Depend<SRV>::instance)
+          throw error::Logic("Attempt to activate an external service implementation, "
+                             "but another instance has already been dependency-injected."
+                            , error::LUMIERA_ERROR_LIFECYCLE);
+        Depend<SRV>::instance = &newInstance;
+      }
+    
+    static void
+    deactivateServiceAccess()
+      {
+        ClassLock<SRV> guard;
+        Depend<SRV>::instance = nullptr;
+      }
+    
     
     
     template<class SUB>
@@ -214,13 +232,42 @@ class DependInject
                             });
       }
     
+    
     template<class IMP>
     class ServiceInstance
       {
+        std::unique_ptr<IMP> instance_;
+        
       public:
         ServiceInstance()
+          : instance_(new IMP{})
           {
-            
+            activateServiceAccess (*instance_);
+          }
+        
+       ~ServiceInstance()
+          {
+            deactivateServiceAccess();
+          }
+        
+        explicit
+        operator bool()  const
+          {
+            return bool(instance_);
+          }
+        
+        IMP&
+        operator* ()  const
+          {
+            ENSURE (instance_);
+            return *instance_;
+          }
+        
+        IMP*
+        operator-> ()  const
+          {
+            ENSURE (instance_);
+            return instance_.get();
           }
       };
     
@@ -256,7 +303,7 @@ struct Dummy
    ~Dummy() { checksum -= N; cout << "~Dummy<"<<N<<">"<<endl;}
     
     virtual int
-    probe()
+    probe()  override
       {
         return N * checksum;
       }
@@ -290,6 +337,35 @@ main (int, char**)
     SHOW_EXPR( Depend<Dum>{}().probe() );
     SHOW_EXPR( checksum );
     
+    struct SubDummy
+      : Dummy<3>
+      {
+        virtual int
+        probe()  override
+          {
+            return -checksum + offset;
+          }
+        
+        int offset = 0;
+      };
+    
+    Depend<Dummy<3>> dep3;
+    SHOW_EXPR( checksum );
+    {
+      DependInject<Dummy<3>>::ServiceInstance<SubDummy> service{};
+      CHECK (service);
+      SHOW_EXPR( checksum );
+      SHOW_EXPR( dep3().probe() );
+      SHOW_EXPR( checksum );
+      service->offset = 5;
+      SHOW_EXPR( dep3().probe() );
+      SHOW_EXPR( checksum );
+    }
+    SHOW_EXPR( checksum );
+    SHOW_EXPR( dep3().probe() );
+    VERIFY_ERROR (LIFECYCLE, DependInject<Dum>::ServiceInstance<SubDummy>{} );
+    SHOW_EXPR( checksum );
+    
     
     cout <<  "\n.gulp.\n";
     
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index a0bf63ce4..535ca26d5 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -26807,8 +26807,10 @@
 </node>
 <node CREATED="1521208257336" ID="ID_1129640741" MODIFIED="1521208261323" TEXT="ServiceInstance">
 <node CREATED="1521208859989" ID="ID_549061661" MODIFIED="1521208874756" TEXT="Lazy-Init-Factory deaktivieren"/>
-<node CREATED="1521208793630" ID="ID_1357481546" MODIFIED="1521208825093" TEXT="Service-Zugang in Depend&lt;Bla&gt; injizieren"/>
-<node CREATED="1521208889297" ID="ID_214019029" MODIFIED="1521208932875" TEXT="Lebenszyklus-Koppelung">
+<node COLOR="#338800" CREATED="1521208793630" ID="ID_1357481546" MODIFIED="1521335430941" TEXT="Service-Zugang in Depend&lt;Bla&gt; injizieren">
+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1521208889297" ID="ID_214019029" MODIFIED="1521335434588" TEXT="Lebenszyklus-Koppelung">
 <richcontent TYPE="NOTE"><html>
   <head>
     
@@ -26823,9 +26825,14 @@
   </body>
 </html>
 </richcontent>
+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1521208943105" ID="ID_295121984" MODIFIED="1521335440371" TEXT="Ownership an &#xfc;bergebener Service-Impl &#xfc;bernehmen">
+<icon BUILTIN="button_ok"/>
+</node>
+<node COLOR="#338800" CREATED="1521208724943" ID="ID_1527628667" MODIFIED="1521335442003" TEXT="smart-ptr-artiger Zugriff auf die Service-Impl">
+<icon BUILTIN="button_ok"/>
 </node>
-<node CREATED="1521208943105" ID="ID_295121984" MODIFIED="1521208976657" TEXT="Ownership an &#xfc;bergebener Service-Impl &#xfc;bernehmen"/>
-<node CREATED="1521208724943" ID="ID_1527628667" MODIFIED="1521208881882" TEXT="smart-ptr-artiger Zugriff auf die Service-Impl"/>
 </node>
 <node CREATED="1521208261887" ID="ID_384054163" MODIFIED="1521208264827" TEXT="Local">
 <node CREATED="1521209044203" ID="ID_1994153994" MODIFIED="1521209058181" TEXT="Closure &#xfc;ber konkreten Ctor"/>
@@ -27006,7 +27013,7 @@
 </node>
 <node COLOR="#338800" CREATED="1521324229082" ID="ID_1398878858" MODIFIED="1521326553373" TEXT="Storage">
 <icon BUILTIN="button_ok"/>
-<node CREATED="1521324240124" ID="ID_1099103129" MODIFIED="1521324253936">
+<node CREATED="1521324240124" ID="ID_1099103129" MODIFIED="1521333223154">
 <richcontent TYPE="NODE"><html>
   <head>
     
@@ -27018,8 +27025,10 @@
   </body>
 </html>
 </richcontent>
+<icon BUILTIN="ksmiletris"/>
 </node>
-<node CREATED="1521324275919" ID="ID_1710451095" MODIFIED="1521324497413" TEXT="sehe aber auch keinen wirklichen Vorteil">
+<node CREATED="1521324275919" ID="ID_1710451095" MODIFIED="1521333231077" TEXT="sehe aber auch keinen wirklichen Vorteil">
+<icon BUILTIN="smiley-neutral"/>
 <node CREATED="1521324529228" ID="ID_1786667023" MODIFIED="1521324543094" TEXT="man mu&#xdf; sich nicht um die de-Allokation k&#xfc;mmern"/>
 <node CREATED="1521324554465" ID="ID_1577416641" MODIFIED="1521324568043" TEXT="Storage ist garantiert vorhanden, kein out-of-Memory"/>
 <node CREATED="1521324668449" ID="ID_1013908061" MODIFIED="1521324682434" TEXT="Meyers Singleton ist elegant und schnell"/>