view: add a method to extract type cast bytes from a view

view.hpp

@@ -588,6 +588,36 @@ namespace util {
     }
 
 
+    ///////////////////////////////////////////////////////////////////////////
+    /// extract a reference to a known type at the front of a byte-view
+    ///
+    /// returns a reference to a value of the designated type at the front of
+    /// the byte-view, or throws an exception if there is insufficient data.
+    ///
+    /// there are no validity or other checks performed on the returned data
+    /// (other than memory safety wrt to the view). this is deliberate, so
+    /// that the function is safe to call on user supplied data during
+    /// parsing routines. it is up to the user to ensure the object is valid.
+    ///
+    /// the buffer object is advanced in place so that it no longer covers
+    /// the extract value
+    template <
+        typename ValueT,
+        typename ByteT,
+        typename = std::enable_if_t<sizeof (ByteT) == 1>
+    >
+    ValueT const&
+    extract (util::view<const ByteT*> &buffer)
+    {
+        if (buffer.size () < sizeof (ValueT))
+            throw std::runtime_error ("insufficient data for view shift");
+
+        ValueT const &res = *reinterpret_cast<ValueT const*> (buffer.data ());
+        buffer = buffer.consume (sizeof (ValueT));
+        return res;
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     template <
         typename BeginA, typename EndA,