Using IEnumerable without foreach loop

问题

I've gotta be missing something simple here.

Take the following code:

public IEnumerable<int> getInt(){
  for(int i = 0; i < 10; i++){
   yield return i;
  }
}

I can call this with:

foreach (int j in obj.getInt()){
  //do something with j
}

How can I use the getInt method without the foreach loop:

IEnumerable<int> iter = obj.getInt();
// do something with iter ??

Thanks.

EDITS

For those wondering why I'd want this. I'm iterating two things:

IEnumerator<int> iter = obj.getInt().GetEnumerator();
foreach(object x in xs){
  if (x.someCondition) continue;
  iter.MoveNext();
  int n = iter.current();
  x.someProp = n;
  etc...
}

回答1:

You can get a reference to the Enumerator, using the GetEnumerator method, then you can use the MoveNext() method to move on, and use the Current property to access your elements:

var enumerator = getInt().GetEnumerator();
while(enumerator.MoveNext())
{
    int n = enumerator.Current;
    Console.WriteLine(n);
}

回答2:

My advice: don't mess around with the enumerators at all. Characterize your problem as a series of operations on sequences. Write code to express those operations. Let the sequence operators take care of managing the enumerators.

So let's see if I've got this straight. You have two sequences. Let's say { 2, 3, 5, 7, 12 } and { "frog", "toad" }. The logical operation you want to perform is, say "go through the first sequence. Every time you find a number divisible by three, get the next item in the second sequence. Do something with the resulting (number, amphibian) pair."

Easily done. First, filter the first sequence:

var filtered = firstSequence.Where(x=>x%3 == 0);

Next, zip the filtered sequence with the second sequence:

var zipped = filtered.Zip(
             secondSequence, 
             (y, z)=> new {Number = x, Amphibian = y});

And now you can iterate over the zipped sequence and do whatever you want with the pairs:

foreach(var pair in zipped)
    Console.WriteLine("{0} : {1}", pair.Number, pair.Amphibian);

Easy peasy, no messing about with enumerators.

回答3:

How about this?

IEnumerator<int> iter = obj.getInt();
using(iter) {
    while(iter.MoveNext()) {
        DoSomethingWith(iter.Current)
    }
}

回答4:

using for loop:

for (var enumerator = getInt().GetEnumerator(); enumerator.MoveNext(); )
{
    Console.WriteLine(enumerator.Current);
}

回答5:

Although the accepted answers are correct, notice that IEnumerator.Current is undefined before the first call to MoveNext().

If you are iterating over a secondary array, you'll want something like:

IEnumerable<Foo> Foo() { ... }

int AssignValues(List<TakesFoo> data) {
  var count = 0;
  var foo = Foo().GetEnumerator();

  // Step into the first element of the array;
  // doing this does not discard a value from the IEnumerator
  if (foo.MoveNext()) { 
    foreach (var x in data) {
      x.SetFoo(foo.Current);
      count += 1;
      if (!foo.MoveNext()) { 
        break;
      }
   }

   // Return count of assigned values
   return count;
}

回答6:

It's important to mention that the duty of the foreach loop is to dispose the enumerator if the instance implements IDisposable. In other words, foreach should be replaced with something like:

var enumerator = enumerable.GetEnumerator();

try
{
    while (enumerator.MoveNext())
    {
        var item = enumerator.Current;
        // do stuff
    }
}
finally
{
    var disposable = enumerator as IDisposable;
    if (disposable != null)
    {
        disposable.Dispose();
    }
}

来源：https://stackoverflow.com/questions/2248985/using-ienumerable-without-foreach-loop

标签

ienumerable

yield-return