При запуске в code::blocks появляются ошибки "<название> was not declared in this scope"

#ifndef LIST_H
#define LIST_H
#include <stdexcept>
#include <cstdlib>
template<class T>
class ListNode {
private:
    ListNode<T>* Next_node;
    T Item;
public:
    ListNode(const T& new_item, ListNode<T>* new_next_node = nullptr) : Item(new_item), Next_node(new_next_node) {}
    ListNode<T>* GetNext() const { return Next_node; }
    T GetItem() const { return Item; }
    void SetNext(ListNode<T>* new_next_node) { Next_node = new_next_node; }
    void SetItem(const T& new_item) { Item = new_item; }
};

template<class T>
class ArraySequence : public Sequence<T> {
private:
    T* Arr;
    int Capacity;
public:
    ArraySequence() : Arr(nullptr), Capacity(0) {}
    ArraySequence(T* new_arr, int length);
    ~ArraySequence() { delete Arr; }
    [COLOR="darkorange"]T Get(int index) const override;[/COLOR]
    ArraySequence<T>& GetSubsequence(int start_index, int end_index) const override;
    void InsertAt(int index, const T& item) override;
    bool Remove(const T& item) override;
};
 
template<class T>
ArraySequence<T>::ArraySequence(T *new_arr, int length) {
    Length = length;
    Capacity = (length / 10 + 1) * 10;
    T* Arr = new T[Capacity];
    for (int i = 0; i < length; ++i)
        Arr[i] = new_arr[i];
}
 
template<class T>
[COLOR="darkorange"] ArraySequence<T>::Get(int index) const {[/COLOR]
    if (index < 0 || index >= Length)
        throw std::range_error("Index is out of range");
    return Arr[index];
}

template<class T>
class ArraySequence : public Sequence<T> {
private:
    T* Arr;
    int Capacity;
public:
    ArraySequence() : Arr(nullptr), Capacity(0) {}
    ArraySequence(T* new_arr, int length);
    ~ArraySequence() { delete[] Arr; } // !!
    T Get(int index) const override;
    ArraySequence<T>& GetSubsequence(int start_index, int end_index) const override;
    void InsertAt(int index, const T& item) override;
    bool Remove(const T& item) override;
};
 
template<class T>
ArraySequence<T>::ArraySequence(T *new_arr, int length) {
    this->Length = length; //!!
    Capacity = (length / 10 + 1) * 10;
    Arr = new T[Capacity]; //!!!
    for (int i = 0; i < length; ++i)
        Arr[i] = new_arr[i];
}
 
template<class T>
T ArraySequence<T>::Get(int index) const { //!!
    if (index < 0 || index >= this->Length) //!!
        throw std::range_error("Index is out of range");
    return Arr[index];
}