CODEWITHSUNDEEP
.netfor-loopienumerator
Data
Data

Reputation: 1357

What is the point of IEnumerator?

This is an excellent video explaining what it is and the differences, but it seems it has a fundamental flaw, you can't skip around the list; it even lacks a Previous() method.

I was sending a list off to a function after if it found a match, instead of the original for...next starting from the next index, i just returned the row of where the next match was found in the function, as it has already done a secondary loop to read all the lines between each 'Hello' block.

I can't do any of this with an iteration class like IEnumerator; am i missing something?

For row As Integer = 0 To dataList.Count - 1
    If row <> -1 Then
       If dataList.Item(row) = "Hello" Then row = SayHello(row)
    End If
Next

Upvotes: 0

Views: 107

Answers (4)

Adam Robinson
Adam Robinson

Reputation: 185663

The purpose of the interface (and the accompanying IEnumerable interface) is to provide a forward-only mechanism for iterating over a collection (or similar structure). Given that, I don't think it's fair to say that it has a "fundamental flaw" because you cannot skip around or go in reverse any more than it would be fair to say that a compact car has a fundamental flaw because you can't use it to transport large farm animals.

Or, for those who may not favor car analogies, it's akin to saying a banana has a fundamental flaw because it (in an ordinary, unfrozen state) cannot be used to pound in nails.

Upvotes: 0

igrimpe
igrimpe

Reputation: 1785

The point of an IEnumerator is to only serve ONE object at a time, which means you can save memory and/or time. To work with a list, you need to fill the list first. Even if you do not really need the complete list, but always use a single item at each iteration.

Private Iterator Function AllIntegers() As IEnumerable(Of Integer)
    Dim i = Integer.MinValue
    While i < Integer.MaxValue
        Yield i
    End While
End Function

Now you could do

For each i in AllIntegers

And now try to put all these integers into a List(Of Integer)

Upvotes: 0

seekerOfKnowledge
seekerOfKnowledge

Reputation: 524

The very definition of enumerating is to mention things one by one. To enumerate is to start at the top and look at each item down the list. That is what enumerating is. So, something that is enumerable would be something that you could look at one by one from the top. The name IEnumerable is very appropriate.

Upvotes: 0

Oded
Oded

Reputation: 499132

you can't skip around the list

You say that's a flaw. It isn't when you don't want to allow skipping around a list.

The number one thing people do with lists is iterate over them - this is the lowest common denominator for collections of all types.

If you do need to skip around, as in your example, don't use IEnumerator.

Upvotes: 2

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