functor: add begin and end convenience transforms

functor.hpp

@@ -12,6 +12,32 @@
 
 
 namespace cruft::functor {
+    /// A trivial functor that wraps std::begin without any static typing.
+    struct begin {
+        template <typename valuet>
+        decltype (auto)
+        operator() (valuet &&value) noexcept (noexcept (std::begin (value)))
+        {
+            return std::begin (
+                std::forward<valuet> (value)
+            );
+        }
+    };
+
+
+    /// A trivial functor that wraps std::end without any static typing.
+    struct end {
+        template <typename valuet>
+        decltype (auto)
+        operator() (valuet &&value) noexcept (noexcept (std::end (value)))
+        {
+            return std::end (
+                std::forward<valuet> (value)
+            );
+        }
+    };
+
+
     ///////////////////////////////////////////////////////////////////////////
     /// returns the value provided at construction time regardless of the
     /// arguments supplied in the call operator.