Allow to cast of trivial values as array of a "smaller" type

This is to be used with caution, since no data is copied. One has to ensure that
the cast data lives longer than the associated CastArray.

This might need to be reworked.

src/utils/CastArray.hpp

@@ -57,6 +57,19 @@ class CastArray
     }
   }
 
+  PASTIS_INLINE
+  CastArray(DataType& value)
+      : m_size  (sizeof(DataType)/sizeof(CastDataType)),
+        m_values(reinterpret_cast<CastDataType*>(&(value)))
+  {
+    static_assert((std::is_const_v<CastDataType> and std::is_const_v<DataType>) or
+                  (not std::is_const_v<DataType>), "CastArray cannot remove const attribute");
+    static_assert(std::is_trivial_v<DataType>, "Defining CastArray from non trivial type is not allowed");
+  }
+
+  PASTIS_INLINE
+  CastArray(DataType&& value) = delete;
+
   PASTIS_INLINE
   CastArray(const CastArray&) = default;
 
@@ -79,4 +92,16 @@ struct cast_array_to
   }
 };
 
+template <typename CastDataType>
+struct cast_value_to
+{
+  template <typename DataType>
+  PASTIS_INLINE
+  static CastArray<DataType, CastDataType>
+  from(DataType& value)
+  {
+    return CastArray<DataType, CastDataType>(value);
+  }
+};
+
 #endif // CAST_ARRAY_HPP