view: use decltype for make_view type deduction

some types will not have iterator typedefs but are capable of providing
iterators. use the types that std::begin and friends return instead of
deducing them ourselves.

view.hpp

@@ -61,11 +61,11 @@ namespace util {
     };
 
     template <typename T>
-    view<typename T::iterator>
+    auto
     make_view (T&);
 
     template <typename T>
-    view<typename T::const_iterator>
+    auto
     make_view (const T&);
 
     template <typename T>

view.ipp

@@ -152,17 +152,17 @@ util::view<T>::operator== (const view<T> rhs) const noexcept
 
 ///////////////////////////////////////////////////////////////////////////////
 template <typename T>
-util::view<typename T::iterator>
+auto
 util::make_view (T &t)
 {
-    return util::view<typename T::iterator> { t.begin (), t.end () };
+    return util::view<decltype(std::begin (t))> { t.begin (), t.end () };
 }
 
 
 //-----------------------------------------------------------------------------
 template <typename T>
-util::view<typename T::const_iterator>
+auto
 util::make_view (const T &t)
 {
-    return util::view<typename T::const_iterator> { t.cbegin (), t.cend () };
+    return util::view<decltype(std::cbegin (t))> { t.cbegin (), t.cend () };
 }