C++11 Vector with move semantics

Question

I am practicing move semantics and placement new by writing a custom Vector class but I am not confident that I use them right. I would really appreciate some pieces of advice regarding my code.

Here is my Vector header

#ifndef VECTOR_VECTOR_H
#define VECTOR_VECTOR_H
#include <iostream>
#include <utility>
#include <iterator>
#include <algorithm>
#define _NOEXCEPT noexcept
template < typename T > class Vector { public: explicit Vector( size_t = INITIAL_CAPACITY );
 Vector( size_t, const T & );
 template < typename InputIterator > Vector( InputIterator, InputIterator );
 Vector( const Vector & );
 Vector( Vector && ) _NOEXCEPT;
 Vector &operator=( const Vector & );
 Vector &operator=( Vector && ) _NOEXCEPT;
 Vector &operator=( std::initializer_list < T > );
 ~Vector();
 template < class InputIterator > void assign( InputIterator first, InputIterator last );
 void assign( size_t n, const T &val );
 void assign( std::initializer_list < T > il );
 void push_back( const T & );
 void push_back( T && );
 void pop_back() _NOEXCEPT;
 void reserve( size_t );
 void resize( size_t );
 void resize( size_t, const T & );
 T &operator[]( size_t );
 const T &operator[]( size_t ) const;
 T &at( size_t );
 const T &at( size_t ) const;
 T &front();
 const T &front() const;
 T &back();
 const T &back() const;
 T *data() _NOEXCEPT;
 const T *data() const _NOEXCEPT;
 bool empty() const _NOEXCEPT;
 size_t size() const _NOEXCEPT;
 size_t capacity() const _NOEXCEPT;
 bool contains( const T & ) const _NOEXCEPT;
 void shrink_to_fit();
 void swap( Vector & );
 void clear() _NOEXCEPT;
#include "const_iterator.h"
#include "iterator.h"
#include "const_reverse_iterator.h"
#include "reverse_iterator.h"
 iterator begin() _NOEXCEPT { return iterator( m_data ); }
 iterator end() _NOEXCEPT { return iterator( m_data + m_size ); }
 reverse_iterator rbegin() _NOEXCEPT { return reverse_iterator( m_data + m_size - 1 ); }
 reverse_iterator rend() _NOEXCEPT { return reverse_iterator( m_data
- 1 ); }
 const_iterator begin() const _NOEXCEPT { return const_iterator( m_data ); }
 const_iterator end() const _NOEXCEPT { return const_iterator( m_data + m_size ); }
 const_reverse_iterator rbegin() const _NOEXCEPT { return const_reverse_iterator( m_data + m_size - 1 ); }
 const_reverse_iterator rend() const _NOEXCEPT { return const_reverse_iterator( m_data - 1 ); }
 const_iterator cbegin() const _NOEXCEPT { return const_iterator( m_data ); }
 const_iterator cend() const _NOEXCEPT { return const_iterator( m_data + m_size ); }
 const_reverse_iterator crbegin() const _NOEXCEPT { return const_reverse_iterator( m_data + m_size - 1 ); }
 const_reverse_iterator crend() const _NOEXCEPT { return const_reverse_iterator( m_data - 1 ); }
 iterator erase( const_iterator );
 iterator erase( const_iterator, const_iterator );
 iterator insert( const_iterator position, const T &val );
 iterator insert( const_iterator position, size_t n, const T &val );
 template < class InputIterator > iterator insert( const_iterator position, InputIterator first, InputIterator last );
 iterator insert( const_iterator position, T &&val );
 iterator insert( const_iterator position, std::initializer_list < T > il );
private: void allocateMemory_( T *&, size_t );
 void moveFrom_( Vector && ) _NOEXCEPT;
 void destructObjects_() _NOEXCEPT;
 bool makeSpace( iterator, size_t );
private: T *m_data; size_t m_size; size_t m_capacity;
 static const int INITIAL_CAPACITY = 2; static const int FACTOR 
= 2; };
template < typename T > bool operator==( const Vector < T > &lhs, const Vector < T > &rhs );
template < typename T > bool operator!=( const Vector < T > &lhs, const Vector < T > &rhs );
template < typename T > bool operator>( const Vector < T > &lhs, const Vector < T > &rhs );
template < typename T > bool operator>=( const Vector < T > &lhs, const Vector < T > &rhs );
template < typename T > bool operator<( const Vector < T > &lhs, const Vector < T > &rhs );
template < typename T > bool operator<=( const Vector < T > &lhs, const Vector < T > &rhs );
#include "vector_implementations.h"
#endif //VECTOR_VECTOR_H

My Vector implementations are in a separate header for readability purposes.

#ifndef VECTOR_VECTOR_IMPLEMENTATIONS_H
#define VECTOR_VECTOR_IMPLEMENTATIONS_H
template < typename T >
inline Vector < T >::Vector( size_t capacity ) :m_data( nullptr ), m_size( 0 ), m_capacity( capacity ) {
 allocateMemory_( m_data, m_capacity );
}
template < typename T >
inline Vector < T >::Vector( const Vector &rhs ) : Vector( rhs . m_size ) {
 std::copy( rhs . begin(), rhs . end(), begin());
}
template < typename T >
inline Vector < T >::Vector( Vector &&rhs ) _NOEXCEPT {
 moveFrom_( std::move( rhs ));
}
template < typename T >
inline Vector < T > &Vector < T >::operator=( const Vector &rhs ) {
 if ( this != &rhs ) {
 //copy-swap idiom
 Vector tmp( rhs );
 swap( tmp );
 }
 return *this;
}
template < typename T >
inline Vector < T > &Vector < T >::operator=( Vector &&rhs ) _NOEXCEPT {
 if ( this != &rhs ) {
 clear();
 moveFrom_( std::move( rhs ));
 }
 return *this;
}
template < typename T >
inline Vector < T >::~Vector() {
 clear();
}
template < typename T >
inline void Vector < T >::pop_back() _NOEXCEPT {
 m_data[ --m_size ] . ~T();
}
template < typename T >
inline void Vector < T >::push_back( const T &element ) {
 if ( !m_data || m_size == m_capacity ) {
 reserve( m_capacity ? m_capacity * FACTOR : INITIAL_CAPACITY );
 }
 new( m_data + m_size )T( element );
 ++m_size;
}
template < typename T >
inline void Vector < T >::push_back( T &&element ) {
 if ( !m_data || m_size == m_capacity ) {
 reserve( m_capacity ? m_capacity * FACTOR : INITIAL_CAPACITY );
 }
 new( m_data + m_size )T( std::move( element ));
 ++m_size;
}
template < typename T >
inline T &Vector < T >::operator[]( size_t idx ) {
 return *( m_data + idx );
}
template < typename T >
inline const T &Vector < T >::operator[]( size_t idx ) const {
 return *( m_data + idx );
}
template < typename T >
inline T &Vector < T >::at( size_t idx ) {
 if ( idx >= m_size ) {
 throw ( std::out_of_range( "Invalid index" ));
 }
 return *( m_data + idx );
}
template < typename T >
inline const T &Vector < T >::at( size_t idx ) const {
 if ( idx >= m_size ) {
 throw ( std::out_of_range( "Invalid index" ));
 }
 return *( m_data + idx );
}
template < typename T >
inline T &Vector < T >::front() {
 return *m_data;
}
template < typename T >
inline const T &Vector < T >::front() const {
 return *m_data;
}
template < typename T >
inline T &Vector < T >::back() {
 return *( m_data + m_size - 1 );
}
template < typename T >
inline const T &Vector < T >::back() const {
 return *( m_data + m_size - 1 );
}
template < typename T >
inline T *Vector < T >::data() _NOEXCEPT {
 return m_data;
}
template < typename T >
inline const T *Vector < T >::data() const _NOEXCEPT {
 return m_data;
}
template < typename T >
inline bool Vector < T >::empty() const _NOEXCEPT {
 return ( m_size == 0 );
}
template < typename T >
inline size_t Vector < T >::size() const _NOEXCEPT {
 return m_size;
}
template < typename T >
inline size_t Vector < T >::capacity() const _NOEXCEPT {
 return m_capacity;
}
template < typename T >
inline bool Vector < T >::contains( const T &element ) const _NOEXCEPT {
 for ( int i = 0 ;
 i < m_size ;
 ++i ) {
 if ( m_data[ i ] == element ) {
 return true;
 }
 }
 return false;
}
template < typename T >
inline void Vector < T >::shrink_to_fit() {
 Vector( *this ) . swap( *this );
}
template < typename T >
inline void Vector < T >::swap( Vector &rhs ) {
 //check ADL look up
 using std::swap;
 swap( m_data, rhs . m_data );
 swap( m_size, rhs . m_size );
 swap( m_capacity, rhs . m_capacity );
}
template < typename T >
inline void Vector < T >::clear() _NOEXCEPT {
 destructObjects_();
 operator delete( m_data );
 m_capacity = 0;
}
template < typename T >
inline void Vector < T >::allocateMemory_( T *&destination, size_t capacity ) {
 destination = static_cast< T * >( operator new[]( capacity * sizeof( T )));
}
template < typename T >
inline void Vector < T >::moveFrom_( Vector &&rhs ) _NOEXCEPT {
 m_data = rhs . m_data;
 rhs . m_data = nullptr;
 m_size = rhs . m_size;
 m_capacity = rhs . m_capacity;
}
template < typename T >
inline void Vector < T >::destructObjects_() _NOEXCEPT {
 while ( !empty()) {
 pop_back();
 }
}
template < typename T >
inline void Vector < T >::reserve( size_t size ) {
 if ( size <= m_capacity ) {
 return;
 }
 T *newData = nullptr;
 allocateMemory_( newData, size );
 size_t i = 0;
 for ( ; i < m_size ;
 ++i ) {
 new( newData + i )T( std::move( m_data[ i ] ));
 }
 clear();
 m_size = i;
 m_data = newData;
 m_capacity = size;
}
template < typename T >
inline void Vector < T >::resize( size_t size ) {
 resize( size, T());
}
template < typename T >
inline void Vector < T >::resize( size_t size, const T &value ) {
 reserve( size );
 if ( size <= m_size ) {
 while ( m_size > size ) {
 pop_back();
 }
 } else {
 while ( m_size < size ) {
 push_back( value );
 }
 }
}
template < typename T >
inline typename Vector < T >::iterator Vector < T >::erase( typename Vector < T >::const_iterator position ) {
 //std::advance(it,std::distance(cbegin(),position));
 //iterator iter = begin() + ( position - cbegin() );
 //std::move( iter + 1, end(), iter );
 //pop_back();
 //return iter;
 return erase( position, position + 1 );
}
template < typename T >
inline typename Vector < T >::iterator Vector < T >::erase
 ( typename Vector < T >::const_iterator first, typename Vector < T >::const_iterator last ) {
 //UB on invalid range
 iterator iter = begin() + ( first - cbegin());
 int removed_elements = last - first;
 std::move( last, cend(), iter );
 while ( removed_elements-- ) {
 pop_back();
 }
 return iter;
}
template < typename T >
bool Vector < T >::makeSpace( Vector::iterator position, size_t space ) {
 size_t elementsToMove = end() - position;
 std::cout << "POSITION " << elementsToMove << std::endl;
 if ( m_size + space >= m_capacity ) {
 reserve( m_capacity ? m_capacity * FACTOR : INITIAL_CAPACITY );
 }
 for ( int i = 0 ;
 i < elementsToMove ;
 ++i ) {
 new( m_data + m_size + space - i ) T( std::move( m_data[ m_size - i ] ));
 }
 m_size += space;
}
template < typename T >
Vector < T >::Vector( size_t n, const T &val ) :Vector( n ) {
 while ( n-- ) {
 push_back( val );
 }
}
template < typename T >
template < typename InputIterator >
Vector < T >::Vector( InputIterator first, InputIterator last ) {
 size_t numElements = last - first;
 allocateMemory_( m_data, numElements );
 while ( first != last ) {
 push_back( *first );
 ++first;
 }
}
template < typename T >
Vector < T > &Vector < T >::operator=( std::initializer_list < T > il ) {
 Vector tmp( il . begin(), il . end());
 swap( tmp );
 return *this;
}
template < typename T >
Vector::iterator Vector < T >::insert( Vector::const_iterator position, const T &val ) {
 size_t offset = position - cbegin();
 makeSpace( begin() + offset - 1, 1 );
 m_data[ offset ] = val;
 return ( begin() + offset );
}
template < typename T >
Vector::iterator Vector < T >::insert( Vector::const_iterator position, size_t n, const T &val ) {
 size_t offset = position - cbegin();
 makeSpace( begin() + offset - 1, n );
 for ( int i = 0 ; i < n ; ++i ) {
 m_data[ offset + i ] = val;
 }
 return ( begin() + offset );
}
template < typename T >
template < class InputIterator >
Vector::iterator Vector < T >::insert( Vector::const_iterator position, InputIterator first, InputIterator last ) {
 size_t offset = position - cbegin();
 makeSpace( begin() + offset - 1, last - first );
 int i = 0;
 while ( first != last ) {
 m_data[ offset + i ] = *first;
 ++first;
 ++i;
 }
 return ( begin() + offset );
}
template < typename T >
Vector::iterator Vector < T >::insert( Vector::const_iterator position, T &&val ) {
 size_t offset = position - cbegin();
 makeSpace( begin() + offset - 1, 1 );
 m_data[ offset ] = std::move( val );
 return ( begin() + offset );
}
template < typename T >
Vector::iterator Vector < T >::insert( Vector::const_iterator position, std::initializer_list < T > il ) {
 return insert( position, il . begin(), il . end());
}
template < typename T >
template < class InputIterator >
void Vector < T >::assign( InputIterator first, InputIterator last ) {
 swap( Vector( first, last ));
}
template < typename T >
void Vector < T >::assign( size_t n, const T &val ) {
 swap( Vector( n, val ));
}
template < typename T >
void Vector < T >::assign( std::initializer_list < T > il ) {
 swap( Vector( il ));
}
template < typename T >
inline bool operator==( const Vector < T > &lhs, const Vector < T > &rhs ) {
 if ( lhs . size() != rhs . size()) {
 return false;
 }
 for ( int i = 0 ;
 i < lhs . size() ;
 ++i ) {
 if ( lhs[ i ] != rhs[ i ] ) {
 return false;
 }
 }
 return true;
}
template < typename T >
inline bool operator!=( const Vector < T > &lhs, const Vector < T > &rhs ) {
 return !( lhs == rhs );
}
template < typename T >
inline bool operator>( const Vector < T > &lhs, const Vector < T > &rhs ) {
 return rhs < lhs;
}
template < typename T >
inline bool operator>=( const Vector < T > &lhs, const Vector < T > &rhs ) {
 return !( lhs < rhs );
}
template < typename T >
inline bool operator<( const Vector < T > &lhs, const Vector < T > &rhs ) {
 int i = 0;
 while ( i < lhs . size() && i < rhs . size() && lhs[ i ] == rhs[ i ] ) {
 ++i;
 }
 if ( i == lhs . size() || i == rhs . size()) {
 return lhs . size() < rhs . size();
 }
 return lhs[ i ] < rhs[ i ];
}
template < typename T >
inline bool operator<=( const Vector < T > &lhs, const Vector < T > &rhs ) {
 return !( rhs < lhs );
}
#endif //VECTOR_VECTOR_IMPLEMENTATIONS_H

And I will just post the code for one of the iterators type, because the rest are identical.

#ifndef VECTOR_CONST_REVERSE_ITERATOR_H
#define VECTOR_CONST_REVERSE_ITERATOR_H
class const_reverse_iterator : public std::iterator<std::random_access_iterator_tag, const T>
{
 friend class Vector;
 friend class const_iterator;
public:
 const_reverse_iterator( const T* data = nullptr ) : m_data( data )
 {}
 const T& operator*() const
 {
 return *m_data;
 }
 const T* operator->() const
 {
 return m_data;
 }
 const_reverse_iterator& operator++()
 {
 --m_data;
 return *this;
 }
 const_reverse_iterator operator++( int )
 {
 const_reverse_iterator res( *this );
 --( *this );
 return res;
 }
 const_reverse_iterator& operator+=( int n )
 {
 while ( --n )
 ++( *this );
 return *this;
 }
 const_reverse_iterator operator+( int n ) const
 {
 const_reverse_iterator tmp( *this );
 tmp -= n;
 return tmp;
 }
 const_reverse_iterator& operator--()
 {
 ++m_data;
 return *this;
 }
 const_reverse_iterator operator--( int )
 {
 const_reverse_iterator res( *this );
 ++( *this );
 return res;
 }
 const_reverse_iterator& operator-=( int n )
 {
 while ( n-- )
 --( *this );
 return *this;
 }
 const_reverse_iterator operator-( int n ) const
 {
 const_reverse_iterator tmp( *this );
 tmp += n;
 return tmp;
 }
 ptrdiff_t operator- ( const const_reverse_iterator& rhs ) const
 {
 return m_data - rhs.m_data;
 }
 const_iterator base()
 {
 return const_iterator( m_data + 1 );
 }
 const T& operator[] ( size_t ind ) const
 {
 return ( *( m_data - ind ) );
 }
 bool operator==( const const_reverse_iterator& other ) const _NOEXCEPT
 {
 return m_data == other.m_data;
 }
 bool operator!=( const const_reverse_iterator& other ) const _NOEXCEPT
 {
 return !( other == *this );
 }
 bool operator<( const const_reverse_iterator& other ) const _NOEXCEPT
 {
 return m_data > other.m_data;
 }
 bool operator>( const const_reverse_iterator& other ) const _NOEXCEPT
 {
 return *this < other;
 }
private:
 const T* m_data;
};
#endif //VECTOR_CONST_REVERSE_ITERATOR_H

• Loki Astari: Ooooh. This is a big NoNo. _NOEXCEPT Leading underscore followed by a capitol letter. Don't do that. In fact why have it at all. We know your code needs to be at least C++11 as it has move semantics built in and C++11 has the keyword noexcept.
• Sᴀᴍ Onᴇᴌᴀ: Please don't edit your code to incorporate advice from answers. I rolled back your last edit. After getting an answer you are not allowed to change your code anymore. This is to ensure that answers do not get invalidated and have to hit a moving target. If you have changed your code you can either post it as an answer (if it would constitute a code review) or ask a new question with your changed code (linking back to this one as reference). Refer to this post for more information
• Peter Cordes: @SᴀᴍOnᴇᴌᴀ: If you look at those changes, they were pure whitespace/formatting that looked like unintentional copy/paste problems or something. Martin York's answer addresses this mess, but I'm not sure it was even intentional in the first place. I mean it seems so obviously bad style that I hope nobody did that on purpose, but it is possible. Maybe the OP can clarify.
• Sᴀᴍ Onᴇᴌᴀ: @peterCordes I thought that at first as well, but then on further inspection I noticed that the member variables had been split, per Martin's advice: "My gosh. private: T *m_data; size_t m_size; size_t m_capacity; One variable per line please."
• Peter Cordes: @SᴀᴍOnᴇᴌᴀ: They commented on Martin's answer that it was a copy/paste glitch. Still unfortunate to waste people's time reviewing an unintentionally badly formatted question, but that damage is already done and the long-term usefulness of this question is probably improved if we let the formatting accidents be fixed.

Answer 1

1. We have consistently misspelt std::size_t.
2. _NOEXCEPT is a reserved identifier and may even be expanded as a macro.
3. We should have an initializer-list constructor - as a guide, construction and assignment argument lists should parallel each other.
4. inline is redundant and just adds clutter.
5. makeSpace() has no return statement.
6. Logging output should go to std::clog, not std::cout.
7. Outside of the class definition, the return type of insert() and other functions must be written as typename Vector<T>::iterator rather than Vector::iterator (or use trailing return type syntax).
8. Don't assume that an input iterator has operator-() (but do provide optimised overloads where std::distance() is usable).
9. We can't use T::operator= to populate uninitialized memory with an object - we need to construct in-place, or use one of the std::uninitialized_copy() family of functions.
10. We don't need moveFrom_() if we implement move construction and assignment using swap().
11. We can simplify copy-assign by implementing it in terms of move-assign (see below).
12. Relational operators could be simpler, if we used std::lexicographical_compare() instead of writing those loops.
13. The contains() member function is equivalent to calling std::find() and comparing the result against an end iterator.
14. There's too much whitespace for my taste - I'd certainly remove that around the . operator, and I suggest grouping related declarations on adjacent lines. Spaces around < and > makes template arguments harder to distinguish from the < and > operators.
15. Inheriting from std::iterator is now deprecated.
16. We could use std::reverse_iterator to create a reverse iterator from a forward iterator.
17. We could use a plain pointer as forward iterator.

---

Regarding the iterators, I successfully replaced those four files with:

using iterator = T*;
using const_iterator = const T*;
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;

We need to also remove the -1 from the reverse begin/end (and we can further simplify):

iterator begin() noexcept { return m_data; }
iterator end() noexcept { return m_data + m_size; }
const_iterator begin() const noexcept { return m_data; }
const_iterator end() const noexcept { return m_data + m_size; }
reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
const_reverse_iterator rbegin() const noexcept { return const_reverse_iterator(end()); }
const_reverse_iterator rend() const noexcept { return const_reverse_iterator(begin()); }
const_iterator cbegin() const noexcept { return begin(); }
const_iterator cend() const noexcept { return end(); }
const_reverse_iterator crbegin() const noexcept { return rbegin(); }
const_reverse_iterator crend() const noexcept { return rend(); }

---

Copy-assign implemented in terms of move-assign:

template<typename T>
inline Vector<T> &Vector<T>::operator=(const Vector& rhs)
{
 return *this = Vector<T>{rhs};
}

We can't implement copy-construct the same way, because passing by value depends on copy-construction, giving us a chicken-and-egg issue!

• user188494: @TobySpeight This surpassed my expectations. Learnt so much! Can't say Thank you enough
• Matthieu M.: The copy-assign version is certainly neat syntax-wise... however it's not as efficient as it could be. If *this happens to have enough capacity for rhs.size() elements, then no allocation should be necessary.
• Toby Speight: Good point @Matthieu
• Deduplicator: @MatthieuM. Well, one should then also look at whether copy-constructing an element can throw.
• Matthieu M.: @Michaela: Yes. So will using a naive for-loop instead of a vectorized copy when T is trivially copyable. There's always room for improvement :) Once you get the broad strokes right, though, unless you have very specific performance requirements... Don't sweat the small stuff. First make sure to get it right, then eliminate "gross" performance issues: (1) algorithmic, (2) memory, and only then start looking into micro-optimizations if it's still needed.

Answer 2

Overall

You need to use namespaces in your code. Nearly everybody and their granddaughter builds a Vector class at some point. So the likelhood of a clash is very high. Build yours into your own namespace (then you get not clashes).

Code Review

This is a good start.

#ifndef VECTOR_VECTOR_H
#define VECTOR_VECTOR_H

But does not look very unique to me (especially since everybody builds a Vector). Add the namespace into this guard and you will have something at least reasonably unique.

Don' do this.

#define _NOEXCEPT noexcept

In addition to _NOEXCEPT being a reserved identifier; why are you trying to obfuscate your code? Just put noexcept out there. Everybody understands it nowadays.

That's a lot to put on one line!

template < typename T > class Vector { public: explicit Vector( size_t = INITIAL_CAPACITY );

In the rest of your code you put an empty line between every function (which I also find annoying) but here you force FOUR different things on a single line. Give the reader a break this needs to be broken up. Also group your methods into logical groups.

OK. This is a good constructor. But do you actually need to specify a default value? Can that not be inferred by the value taking on the default constructed version of the type?

 Vector( size_t, const T & );
 // I would have done
 Vector(size_t size, T const& init = T{});

I wish you would break the template stuff onto one row and the method stuff onto another row. That's a more common way of writing these declarations.

 template < typename InputIterator > Vector( InputIterator, InputIterator );

OK. I see assignment to an initializer list but given this why can't I construct the vector with an initializer list? (削除) While we are at it why do you pass initializer lists by value? (削除ここまで)See comments below.

 Vector &operator=( std::initializer_list < T > );
 void assign( std::initializer_list < T > il );

Nice Standard set of push operations.

 void push_back( const T & );
 void push_back( T && );
 void pop_back() _NOEXCEPT;

But why don't I see an emplace_back() in the same area? Am I going to find it below?

Including other header files inside a class (and thus probably a namespace). That's not a disaster waiting to happen (sarcasm). These header files are dependent on this header file. What happens if a user includes them directly. You should at least set up some header guards that makes it hard to do that accidentally.

#include "const_iterator.h"
#include "iterator.h"
#include "const_reverse_iterator.h"
#include "reverse_iterator.h"

Don't really think you need any special iterator classes for a vector. A pointer to the member should work just fine (assuming contiguous memory for the data).

 iterator begin() _NOEXCEPT { return iterator( m_data ); }
 iterator end() _NOEXCEPT { return iterator( m_data + m_size ); }

My gosh.

private: T *m_data; size_t m_size; size_t m_capacity;

One variable per line please. Also brave of you to use T* as the pointer type. Let's see if you get the allocation correct.

Not sure why these are standalone methods. Why are they not members of the class?

template < typename T > bool operator==( const Vector < T > &lhs, const Vector < T > &rhs ); 
template < typename T > bool operator!=( const Vector < T > &lhs, const Vector < T > &rhs ); 
template < typename T > bool operator>( const Vector < T > &lhs, const Vector < T > &rhs ); 
template < typename T > bool operator>=( const Vector < T > &lhs, const Vector < T > &rhs ); 
template < typename T > bool operator<( const Vector < T > &lhs, const Vector < T > &rhs ); 
template < typename T > bool operator<=( const Vector < T > &lhs, const Vector < T > &rhs );

OK. Copy swap idiom usually does not check for self-assignment.

template < typename T >
inline Vector < T > &Vector < T >::operator=( const Vector &rhs ) {
 if ( this != &rhs ) {
 //copy-swap idiom
 Vector tmp( rhs );
 swap( tmp );
 }
 return *this;
}

Yes. A self-assignment check will save you a lot if you actually do a self-assignment. But self-assignment is so vanishingly rare that you are actually pessimizing the normal action. Now this pessimization is a small cost but done so very frequently that the overall cost is on average higher than the cost of a self-assignment copy.

Prob(SelfAssigment) * {Cost Of SelfAssigment} < Prob(NormAssigment) * {Cost Of NormAssigment}

The standard way of writing this is:

// Pre Move semantics.
template < typename T >
inline Vector < T > &Vector < T >::operator=(Vector rhs) {
 swap( rhs );
 return *this;
}
// Post Move semantics as passing by value and RValue ref causes
// conflicting definitions for the compiler.
template < typename T >
inline Vector < T > &Vector < T >::operator=(Vector const& rhs) {
 Vector tmp(rhs);
 swap( tmp );
 return *this;
}

• user188494: 1. I havent actually written my code like that with 1000 stuff on one line. It just got reformatted when I copied-pasted. I will fix it now. 2.I have heard it's a good practice to overload some operators as non-member functions. E.g [stackoverflow.com/questions/29999932/… 3. I think emplace_back should use variadic template arguments, something I havent read anything about yet, which is why it is not there.
• Toby Speight: Non-member comparison operators do make sense, according to the common guideline (they can be implemented using the public interface, so don't make them members).
• Deduplicator: std::initializer_list is a reference type, and always passed by value, unless perfect forwarding interferes. The comparison-operators are probably not members because there is no need for them to be. Also, it allows for more flexibility when allocator-support is added later.
• Deduplicator: Copy-assignment with move-semantics: return *this = Vector(rhs);.