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What is the C # iterator, many beginners are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

The iterator pattern is an example of a behavioral pattern (behavioralpattern) in a design pattern. It is a pattern that simplifies communication between objects and is very easy to understand and use. Simply put, the iterator pattern allows you to get all the elements in a sequence regardless of whether their type is array,list,linkedlist or any other sequence structure. This makes it possible to build a data processing channel (datapipeline) very efficiently-that is, the data can enter the processing channel, perform a series of transformations, or filter, and get the results. In fact, this is the core model of LINQ.

In .NET, the iterator pattern is encapsulated by IEnumerator and IEnumerable and their corresponding generic interfaces. If a class implements the IEnumerable interface, it can be iterated; calling the GetEnumerator method returns the implementation of the IEnumerator interface, which is the iterator itself. An iterator is similar to a cursor in a database. It is a position record in a data sequence. Iterators can only move forward, and multiple iterators in the same data sequence can operate on the data at the same time.

Support for iterators in foreach statements

Support for iterators has been built into C # 1, which is the foreach statement. Making it possible to iterate over the collection more directly and simply than the for loop statement, the compiler compiles the foreach to call the GetEnumerator and MoveNext methods and the Current property, and if the object implements the IDisposable interface, the iterator is released after the iteration is complete. But in Clover 1, implementing an iterator is a relatively tedious operation. Clip2 makes this work much easier and saves a lot of work on implementing iterators.

Suppose we need to implement a new collection type based on ring buffering. We will implement the IEnumerable interface so that users can easily take advantage of all the elements in the collection. We ignore other details and focus only on how to implement the iterator. The set stores the value in the array, and the set can set the starting point of the iteration. for example, if the set has five elements and you can set the starting point to 2, then the iterative output is 2, 3, 4, 0, and finally 1.

Since we set the starting point to 3, the result of the set output is dpenery, a, and b and c

GetEnumerator method

We haven't implemented the GetEnumerator method yet, but how to write the logic of the GetEnumerator part, the first is to store the current state of the cursor somewhere. On the one hand, the iterator pattern does not return all the data at a time, but the client requests only one data at a time. This means that we have to record which record the customer is currently requesting to the collection. The Clear2 compiler has done a lot of work for us to save the state of iterators.

Now let's take a look at which states to save and where to store them. Imagine that we try to save the state in the IterationSample collection so that it implements the IEnumerator and IEnumerable methods. At first glance, it seems possible that, after all, the data is in the right place, including the starting position. Our GetEnumerator method simply returns this. But there is an important problem with this approach: if the GetEnumerator method is called multiple times, multiple independent iterators will return. For example, we can use two nested foreach statements to get all possible value pairs. These two iterations need to be independent of each other. This means that the two iterator objects we need to return each time we call GetEnumerator must remain separate. We can still do this directly in the IterationSample class through the corresponding function. But our class has multiple responsibilities, and this one violates the principle of single responsibility.

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