Require TSource to be a Range (aka Container).

src/cinq_enumerable.hpp

@@ -25,25 +25,29 @@ namespace cinq
          * @param source the source container which
          * provides the data cinq operates on
          */
-         enumerable(){
-           is_data_copied=false;
-
-         }
-
-        enumerable(TSource& source) // requires Container<TSource>()
+        enumerable(TSource& source) requires Range<TSource>()
         {
             is_data_copied = false;
             begin = source.cbegin();
             end = source.cend();
         }
 
-        enumerable(TSource&& source) // requires Container<TSource>()
+        enumerable(TSource&& source) requires Range<TSource>()
         {
             is_data_copied = false;
             begin = source.cbegin();
             end = source.cend();
         }
-
+
+    private:
+
+        enumerable()
+        {
+           is_data_copied=false;
+        }
+
+    public:
+
         /**
          * @brief Filters a sequence of values based on a predicate.
          * Each element's index may be used in the logic of the predicate function.
@@ -920,10 +924,9 @@ namespace cinq
      * @return constructs a type enumerable from the container
      */
     template <typename T>
-    //requires Container<T>()
+    requires Range<T>()
     auto from(T& source)
     {
-        //enumerable<decltype(source.cbegin())> e(source);
         enumerable<T> e(source);
         return e;
     }

src/cinq_test.cpp

@@ -82,6 +82,15 @@ vector<test> make_tests()
         return (result == answer);
     }));
 
+    tests.push_back(test("where() with std::string", []
+    {
+        string s = "C++ INtegrated Query";
+        auto result = cinq::from(s)
+                      .where([](auto& x) { return 'A' < x && x < 'Z'; })
+                      .to_vector();
+        return (result == vector<char>({ 'C', 'I', 'N', 'Q' }));
+    }));
+
     tests.push_back(test("where() with index std::vector", []
     {
         std::vector<int> my_vector { 0, 1, 2, 3, 4 };
@@ -92,7 +101,6 @@ vector<test> make_tests()
         return (result == answer);
     }));
 
-
     tests.push_back(test("where() with index std::list", []
     {
         std::list<int> my_list { 0, 1, 2, 3, 4 };

src/custom_concepts.hpp

@@ -7,8 +7,6 @@
 
 using namespace origin;
 
-//TODO:Container concept
-
 template<typename _Iter>
     concept bool Sortable()
     {