TransposedArray: Define virtual destructor in .cpp file

This fixes compiler warnings from clang:

src/lstm/weightmatrix.h:33:7: warning:
 'TransposedArray' has no out-of-line virtual method definitions;
 its vtable will be emitted in every translation unit [-Wweak-vtables]

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/lstm/weightmatrix.cpp

@@ -46,6 +46,11 @@ void TransposedArray::Transpose(const GENERIC_2D_ARRAY<double>& input) {
   for (int t = 0; t < width; ++t) WriteStrided(t, input[t]);
 }
 
+// Destructor.
+// It is defined here, so the compiler can create a single vtable
+// instead of weak vtables in every compilation unit.
+TransposedArray::~TransposedArray() = default;
+
 // Sets up the network for training. Initializes weights using weights of
 // scale `range` picked according to the random number generator `randomizer`.
 int WeightMatrix::InitWeightsFloat(int no, int ni, bool use_adam,

src/lstm/weightmatrix.h

@@ -36,6 +36,7 @@ class TransposedArray : public GENERIC_2D_ARRAY<double> {
   void Transpose(const GENERIC_2D_ARRAY<double>& input);
   // Writes a vector of data representing a timestep (gradients or sources).
   // The data is assumed to be of size1 in size (the strided dimension).
+  virtual ~TransposedArray();
   void WriteStrided(int t, const float* data) {
     int size1 = dim1();
     for (int i = 0; i < size1; ++i) put(i, t, data[i]);