为什么这个 c++ 代码不能在 g++ 4.8.2 中编译

>我正在尝试使用 g++ 4.8.2（Ubuntu 14.04 环境）编译C++脉冲国际象棋引擎 [0]。

我在链接阶段收到以下错误：

Linking CXX executable pulse-
CMakeFiles/pulse.dir/main.cpp.o: In function `pulse::MoveGenerator::MoveGenerator()':
/home/user/cpp/movegenerator.h:15: undefined reference to `pulse::MoveList<pulse::MoveEntry>::MoveList()'
libcore.so: undefined reference to `pulse::MoveList<pulse::MoveEntry>::rateFromMVVLVA()'
libcore.so: undefined reference to `pulse::MoveList<pulse::RootEntry>::sort()'
libcore.so: undefined reference to `pulse::MoveList<pulse::RootEntry>::MoveList()'
libcore.so: undefined reference to `pulse::MoveList<pulse::MoveEntry>::sort()'
collect2: error: ld returned 1 exit status

当我运行命令时：

g++ -std=c++11 -c movelist.cpp && nm movelist.o | grep sort

我得到输出

0000000000000000 W _ZN5pulse8MoveListINS_9MoveEntryEE4sortEv
0000000000000000 W _ZN5pulse8MoveListINS_9RootEntryEE4sortEv

4.9.1 时，但使用 4.8.2 时没有输出。

为什么 g++ 4.9.1 生成排序函数而 4.8.2 没有，是编译器中的错误还是脉冲源代码中的错误？

编辑：

正如指出的重复问题"为什么模板只能在头文件中实现？"中所述，我不明白，它在 g++ 4.9.1 中是如何工作的？移动列表标头：

#include "value.h"
#include "move.h"
#include <array>
#include <memory>
namespace pulse {
/**
 * This class stores our moves for a specific position. For the root node we
 * will populate pv for every root move.
 */
template<class T> 
class MoveList {
private:
  static const int MAX_MOVES = 256;
public:
  std::array<std::shared_ptr<T>, MAX_MOVES> entries;
  int size = 0; 
  MoveList();
  void sort();
  void rateFromMVVLVA();
};
class MoveVariation {
public:
  std::array<int, Depth::MAX_PLY> moves;
  int size = 0; 
};
class MoveEntry {
public:
  int move = Move::NOMOVE;
  int value = Value::NOVALUE;
};
class RootEntry : public MoveEntry {
public:
  MoveVariation pv;
};
}

移动列表源：

#include "movelist.h"
#include <cassert>
namespace pulse {
template class MoveList<MoveEntry>;
template class MoveList<RootEntry>;
template<class T>
MoveList<T>::MoveList() {
  for (unsigned int i = 0; i < entries.size(); ++i) {
    entries[i] = std::shared_ptr<T>(new T());
  }  
}
/**
 * Sorts the move list using a stable insertion sort.
 */
template<class T> 
void MoveList<T>::sort() {
  for (int i = 1; i < size; ++i) {
    std::shared_ptr<T> entry(entries[i]);
    int j = i; 
    while ((j > 0) && (entries[j - 1]->value < entry->value)) {
      entries[j] = entries[j - 1];
      --j;
    }  
    entries[j] = entry;
  }  
}
/**
 * Rates the moves in the list according to "Most Valuable Victim - Least Valuable Aggressor".
 */
template<class T> 
void MoveList<T>::rateFromMVVLVA() {
  for (int i = 0; i < size; ++i) {
    int move = entries[i]->move;
    int value = 0; 
    int piecetypeValue = PieceType::getValue(Piece::getType(Move::getOriginPiece(move)));
    value += PieceType::KING_VALUE / piecetypeValue;
    int target = Move::getTargetPiece(move);
    if (Piece::isValid(target)) {
      value += 10 * PieceType::getValue(Piece::getType(target));
    }
    assert(value >= (PieceType::KING_VALUE / PieceType::KING_VALUE)
      && value <= (PieceType::KING_VALUE / PieceType::PAWN_VALUE) + 10 * PieceType::QUEEN_VALUE);
    entries[i]->value = value;
  }
}

[0] https://github.com/fluxroot/pulse/tree/master/src/main/cpp