Add the conv_to file from ensmallen

Signed-off-by: Omar Shrit <omar@avontech.fr>

src/mlpack/core.hpp

@@ -37,6 +37,7 @@
 // Now the core mlpack classes.
 #include <mlpack/core/util/arma_traits.hpp>
 #include <mlpack/core/util/ens_traits.hpp>
+#include <mlpack/core/util/conv_to.hpp>
 #include <mlpack/core/util/log.hpp>
 #include <mlpack/core/util/io.hpp>
 #include <mlpack/core/util/deprecated.hpp>

src/mlpack/core/util/conv_to.hpp

@@ -0,0 +1,62 @@
+/**
+ * @file core/util/conv_to.hpp
+ * @author Marcus Edel
+ *
+ * A simple `conv_to` wrapper that based on the data type forwards to
+ * `coot::conv_to` or `arma::conv_to`. This file is borrowed from ensmallen.
+ *
+ * mlpack is free software; you may redistribute it and/or modify it under the
+ * terms of the 3-clause BSD license.  You should have received a copy of the
+ * 3-clause BSD license along with mlpack.  If not, see
+ * http://www.opensource.org/licenses/BSD-3-Clause for more information.
+ */
+#ifndef MLPACK_CORE_UTIL_CONV_TO_HPP
+#define MLPACK_CORE_UTIL_CONV_TO_HPP
+
+namespace mlpack {
+
+/**
+ * A utility class that based on the data type forwards to `coot::conv_to` or
+ * `arma::conv_to`.
+ *
+ * @tparam OutputType The data type to convert to.
+ */
+template<typename OutputType>
+class conv_to
+{
+  public:
+
+#ifdef MLPACK_HAS_COOT
+
+    /**
+    * Convert from one matrix type to another by forwarding to `coot::conv_to`.
+    *
+    * @param input The input that is converted.
+    */
+   template<typename InputType>
+   inline static typename std::enable_if<
+      !arma::is_arma_type<InputType>::value, OutputType>::type
+   from(const InputType& input)
+   {
+     return coot::conv_to<OutputType>::from(input);
+   }
+
+#endif
+
+   /**
+    * Convert from one matrix type to another by forwarding to `arma::conv_to`.
+    *
+    * @param input The input that is converted.
+    */
+   template<typename InputType>
+   inline static typename std::enable_if<
+      arma::is_arma_type<InputType>::value, OutputType>::type
+   from(const InputType& input)
+   {
+     return arma::conv_to<OutputType>::from(input);
+   }
+};
+
+} // namespace mlpack
+
+#endif