helper to pull all elements from an iterator, yielding the last one

src/lib/itertools.hpp

@@ -289,7 +289,7 @@ namespace lib {
         {
           return (cached_ && isOK_)
               || (cached_ = true
-                 &&(isOK_ = predicate_(*Raw::pipe())));            
+                 &&(isOK_ = predicate_(*Raw::pipe())));
         }
       
       void
@@ -540,6 +540,31 @@ namespace lib {
   }
   
   
+  template<class IT>
+  inline typename IT::value_type
+  pull_last (IT iter)
+    {
+      typedef typename IT::value_type Val;
+      typedef wrapper::ItemWrapper<Val> Item;
+      
+      Item lastElm;
+      
+      while (iter)
+        {
+          lastElm = *iter;
+          ++iter;
+        }
+      
+      if (lastElm)
+        return *lastElm;
+      else
+        throw lumiera::error::State ("attempt to retrieve the last element "
+                                     "of an exhausted or empty iterator"
+                                    ,lumiera::error::LUMIERA_ERROR_ITER_EXHAUST);
+    }
+  
+  
+  
   /** filters away repeated values
    *  emitted by source iterator */
   template<class IT>

tests/lib/itertools-test.cpp

@@ -23,6 +23,7 @@
 
 
 #include "lib/test/run.hpp"
+#include "lib/test/test-helper.hpp"
 #include "lib/util.hpp"
 #include "lib/util-foreach.hpp"
 
@@ -47,6 +48,8 @@ namespace test{
   using std::endl;
   using std::rand;
   
+  using lumiera::error::LUMIERA_ERROR_ITER_EXHAUST;
+  
   
   
   namespace { // Test data
@@ -110,6 +113,8 @@ namespace test{
           verify_filterRepetitions();
           
           buildTransformingIterator (source.begin());
+          
+          verifyPullLast(source.begin());
         }
       
       
@@ -253,6 +258,17 @@ namespace test{
         }
       
       
+      void
+      verifyPullLast(Iter const& ii)
+        {
+          Iter::value_type lastElm = pull_last (ii);
+          CHECK (1 == lastElm);     // TestSource holds a decreasing sequence of numbers ending with 1
+          
+          Iter emptyIterator;
+          CHECK (isnil (emptyIterator));
+          
+          VERIFY_ERROR (ITER_EXHAUST, pull_last(emptyIterator) );
+        }
     };
   
   LAUNCHER (IterTools_test, "unit common");