C# CONCEPTS
According to Gang of Four, the iterator pattern provides a process to obtain the aggregator object without knowing its implementation.
Use Case
Let us take an example of a collection list of cars and string[] an array of motorcycles, we need to design an aggregator object so that one can iterate over the collection without knowing whether it’s a list or an array.
The iterator design pattern helps solve this problem wherein a standard iterator will traverse different collection types.
Prerequisites
- Basic knowledge of OOPS concepts.
- Any programming language knowledge.
The article demonstrates the usage of iterator design patterns using the C# programming language. So, to begin with, C#
Getting Started
Considering the above use case, let us define a custom iterator interface that acts as an abstract layer over the list and array iterator.
public interface IVehicleIterator{
void First();
bool IsDone();
string Next();
string Current();
}
Now write car and motorcycle iterators that implement the above interface according to the use case.
CarIterator.cs
The car iterator is implemented over List<string> collection and provides an implementation of interface methods.
https://gist.github.com/ssukhpinder/cd742cc7861c7860a1999178146293c9
MotorcycleIterator.cs
The motorcycle iterator is implemented over string[] collection and provides an implementation of interface methods.
https://gist.github.com/ssukhpinder/23a762f13904d99498f739a18365db90
After all the above iterators are defined, define a standard aggregator object interface that creates iterators.
public interface IVehicleAggregate{
IVehicleIterator CreateIterator();
}
Finally, write down the classes which implement the above aggregator interface. According to the use-case, both Car and Motorcycle classes will implement the aggregator interface.
Car.cs
The method of aggregator interface returns the relevant iterator as shown below.
https://gist.github.com/ssukhpinder/d3d92da9552c1d791800f97b9c81eb7e
Motorcycle.cs
The method of aggregator interface returns the relevant iterator as shown below.
https://gist.github.com/ssukhpinder/84c9fea82b711010cb0ddd05b2bd7b30
Iterator Pattern in Action
https://gist.github.com/ssukhpinder/54831ccaf9f7ecbfc341e27265b9e747
The PrintVehicles methods check if !iterator.isDone then output the collection element. No matter what collection we’re dealing with, implement methods like First, IsDone, and Next.
Output
We don’t know the underlying collection type, but it is still iterated over it via Iterator Design Pattern. If you go ahead and run, it displays the following output.
GitHub Sample Repo
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