Iterator

[Tony Johansson]

Hello!


Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

//Tony

 

[Alf P. Steinbach]

* Tony Johansson:

Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

ArrayList is not a standard class, so no answer is possible.

 

[Rapscallion]

ArrayList is not a standard class

It is - in Java

 

[Ioannis Vranos]

Hello!


Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

When the container contents can be accessed efficiently with indices, then indices are
provided. Consider vector, valarray, bitset, etc.

 

[Andrew McDonagh]

Rapscallion wrote:




Just out of interest: What is it? An array or a list?

List is the interface (i.e. Java's pure abstract class 'like' construct)
http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html


An ArrayList is an implementation of the List interface which is backed
by an array - so 'get(int position)' maps nicely to 'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.

 

[Rolf Magnus]

It is - in Java

Just out of interest: What is it? An array or a list?

 

[Ioannis Vranos]

An ArrayList is an implementation of the List interface which is backed
by an array - so 'get(int position)' maps nicely to 'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.

So, what has it to do with C++? C++ vector provides both random access iterators and
indices. Under .NET, in VS 2005, a managed vector version inheriting from .NET IList<T>
interface will also be provided.

 

[Andrew McDonagh]

An ArrayList is an implementation of the List interface which is
backed by an array - so 'get(int position)' maps nicely to
'array[position]'

There's also LinkedList - which implements the List interface using a
doubly linked list.

So, what has it to do with C++?

Absolutely nothing, I was just answering Rolf's question.

C++ vector provides both random access
iterators and indices.

Great aren't they.

Under .NET, in VS 2005, a managed vector version
inheriting from .NET IList<T> interface will also be provided.

What's this got to do with standard C++ ?

 

[Ioannis Vranos]

Absolutely nothing, I was just answering Rolf's question.

My mistake, I thought you were the original poster.

 

[Cy Edmunds]

Hello!


Why should an Iterator be used instead of using index when going through a
collection for example ArrayList

//Tony

There may or not be a speed advantage, but there is almost certainly a
maintainability advantage if your algorithms don't actually need
subscripting. Consider:

#include <vector>
typedef std::vector<double> t_coll;
t_coll c;
....
for (t_coll::iterator i = c.begin(); i != c.end(); ++i)
*i = 2.2;

Now let's say that after some new requirements come in you find that you
must frequently delete items from the middle of your collection. You need to
use a list instead of a vector for efficient performance. No problem:

#include <list> // change this
typedef std::list<double> t_coll; // and this
t_coll c; // same
....
for (t_coll::iterator i = c.begin(); i != c.end(); ++i) // same
*i = 2.2; // same

Now if you had written you loops as

for (unsigned i = 0; i < c.size(); ++i)
c = 2.2;

you would have to change them all.