I assume that you are familiar with std::queue and std::deque and wrote this class as a reinventing-the-wheel exercise.

There are a few mainly aesthetic points that you could improve:

• int size() is better if returning a std::size_t, which is the underlaying type returned by vector::size().

• Keep parameter names in function prototypes, it helps self-documenting the code.

• T peek() doesn't change any internal state, so it should be const too.

• operator[] should be provided with two overloads, const and non-const:

    T& operator[](std::size_t index);
    const T& operator[](std::size_t index) const;
  

Otherwise you won't be able to access data in a const Queue<T>. The same thing applies to begin()/end(). You will have to provide both const and non-const versions. This is purely boilerplate code, but C++ doesn't offer a better solution.

• This excessively long name: typename std::vector <T>::iterator should be replaced by a typedef or using alias:

    using iterator = std::vector<T>::iterator;
  
    // Then you simply use `iterator` now:
    iterator begin() { ... }
  

• Shouldn't you provide a constructor that takes no arguments? It is very likely that you will want to declare an empty queue at some point. A default constructor should also do:

    Queue() = default;
  

I assume that you are familiar with std::queue and std::deque and wrote this class as a reinventing-the-wheel exercise.

There are a few mainly aesthetic points that you could improve:

• int size() is better if returning a std::size_t, which is the underlying type returned by vector::size().

• Keep parameter names in function prototypes, it helps self-documenting the code.

• T peek() doesn't change any internal state, so it should be const too.

• operator[] should be provided with two overloads, const and non-const:

    T& operator[](std::size_t index);
    const T& operator[](std::size_t index) const;
  

Otherwise you won't be able to access data in a const Queue<T>. The same thing applies to begin()/end(). You will have to provide both const and non-const versions. This is purely boilerplate code, but C++ doesn't offer a better solution.

• This excessively long name: typename std::vector <T>::iterator should be replaced by a typedef or using alias:

    using iterator = std::vector<T>::iterator;
  
    // Then you simply use `iterator` now:
    iterator begin() { ... }
  

• Shouldn't you provide a constructor that takes no arguments? It is very likely that you will want to declare an empty queue at some point. A default constructor should also do:

    Queue() = default;