尝试使用该自定义类中的变量创建自定义类的优先级队列

Question

所以这是我的类，目标是使bnode<symbol>的优先级队列按顺序排列，以便具有最低计数的符号的bnode具有最高优先级。这是我的代码：

struct symbol {
    explicit symbol(char av = 0, int ac = 0) : value(av), count(ac) { }
    char value; // actual symbol, by default 0 (empty)
    int count;  // count of the symbol, by default 0
}; // symbol

// compare two symbols
// symbol with a lower count is "less than" symbol with a higher count
inline bool operator<(const symbol& lhs, const symbol& rhs) {
    return ((lhs.count < rhs.count) || (!(rhs.count < lhs.count) && (lhs.value < rhs.value)));
} // operator<

template <typename T> struct bnode {
    explicit bnode(const T& t = T(), bnode* l = 0, bnode* r = 0)
        : value(t), left(l), right(r) { }

    T value;      // payload

    bnode* left;  // left child
    bnode* right; // right child
}; // struct bnode

#endif // SYMBOL_HPP

//and here is me trying to make a priority queue:
std::priority_queue<bnode<symbol>,std::vector<bnode<symbol> >, std::less<std::vector<bnode<symbol> >::value_type::value> > queue;

/*this results in the error: error: ‘bnode<symbol>::value’ cannot appear in a constant-expression*/