I'm new to C#, just a question on how to use IComparable and IComparer properly. Let's say we have the following class:
public class Student
{
int score;
string name;
}
and I want to sort by socre (desc) first then sort by name (asc).
Now assume that I can't access to the Student class, so I can only use IComparer
so I have to make one help class(let's say it is called StudentComparer) and put the same logic into
public class StudentComparer: IComparer
{
int Compare(object o1, object o2)
{
Student s1 = o1 as Student;
Student s2 = o2 as Student;
// not checking null for simplicity
if (s1.score == s2.score)
return String.Compare(s1.name, s2.name);
else if (s1.score < s2.score)
return -1
else
return 1
}
}
Here is my question, if I just need to use a single rule later, for example, sometimes just sort by name and sometimes just sort by score. So I have to make another two help classes(ScoreComparer and NameComparer) that implement IComparer, which have duplicated code in StudentComparer as
public class ScoreComparer : IComparer
{
int Compare(object o1, object o2)
{
//half logic of StudentComparer
}
}
public class NameComparer: IComparer
{
int Compare(object o1, object o2)
{
//half logic of StudentComparer
}
}
my case is pretty simple, image that if there is a complicated case, each comparer consist of hundreds line of code,so how can I avoid duplicated code? or is it a way to combine multiple Comparer A, B, C, D ... into a common Comparer so that it check A,B,C,D in sequence, just like order by clause in SQL
Back in the days before linq, I used to use comparers a lot.
The way I've handled different sort options was by specifying these options in the constructor of the comparer implementation and then use that information in the Compare method.
Lucky for us, we now have linq so this entire thing can be done with a single, fluent line of code:
// sortedStudents is an IEnumerable<Student> sorted by score and name.
var sortedStudents = students.OrderBy(s => s.Score).ThenBy(s => s.Name);
However, if for some reason you need to work the old-fashion way, using comparers and stuff like that, here is how I would handle this back then:
internal enum CompareBy
{
NameOnly,
ScoreAndName
}
public class StudentComparer: IComparer<Student>
{
private CompareBy _compareBy
public StudentComparer(CompareBy compareBy)
{
_compareBy = compareBy;
}
public int Compare(Student s1, Student s2)
{
// not checking null for simplicity
var nameCompare = string.Compare(s1.name, s2.name);
if(_compareBy == NameOnly)
{
return nameCompare;
}
// since there are only two members in the enum it's safe to write it like this.
// if the enum grows, you must change the code.
if (s1.score == s2.score)
{
return nameCompare;
}
else if (s1.score < s2.score)
{
return -1
}
return 1
}
}
Is there a way to remember the position of an enumerator?
I want to remember the position of an enumerate, so that I can reset it to a position before the current. I don't want to go back to the beginning so .reset() doesn't help.
Btw, is it possible to let the enumerator start eg at the 2. position?
List<string> list = new List<string>(new string[] { "a", "b", "c" });
IEnumerator<string> i = list.GetEnumerator();
i.MoveNext(); richTextBoxOutput.AppendText(i.Current);
IEnumerator<string> t = i; // how do I make a real copy i?
i.MoveNext(); richTextBoxOutput.AppendText(i.Current);
i = t;
i.MoveNext(); richTextBoxOutput.AppendText(i.Current);
As you already have a List<> why don't you maintain an indexer/counter then use the IEnumerable Skip() extension method (and possibly combine that with Take() followed by ForEach()).
Some possibly useful further info:
MSDN: Return Or Skip Elements in a Sequence
Stack Overflow: LINQ with Skip and Take
Is there a way to remember the position of an enumerator?
Sometimes. It depends on how the enumerator is implemented.
In this case the enumerator is implemented as a mutable struct, which was a performance optimisation that people more often run into when it produces this "freeze position" behaviour in situations where they don't want it. (If you're ever writing a generic class that wraps an implementation of IEnumerable<T> then either hold that reference as the interface type rather than the type itself, or don't have it readonly even if it seems like it should be, if you do you can end up with such a struct enumerator permanently frozen).
Just change your code so that instead of:
IEnumerator<string> i = list.GetEnumerator();
…
IEnumerator<string> t = i;
You have either:
List<string>.Enumerator i = list.GetEnumerator();
…
List<string>.Enumerator t = i;
Or simply:
var i = list.GetEnumerator();
…
var t = i;
Now you have i and t defined in terms of this struct and copying from one to the other copies the struct rather than just the reference to the boxed struct.
This will not work with all enumerators, and for that matter it isn't the best way to deliberately make it available when writing your own enumerator (if you needed to do so you'd be better adding some sort of Clone() or Snapshot() method to an enumerator that was a class rather than a struct), but it will work with List<T>.
A more flexible solution that doesn't depend on such a quirk of implementation would be:
public class SnapshotableListEnumerator<T> : IEnumerator<T>
{
private readonly IList<T> _list;
private int _idx;
private SnapshotableListEnumerator(IList<T> list, int idx)
{
_list = list;
_idx = idx;
}
public SnapshotableListEnumerator(IList<T> list)
: this(list, -1)
{
}
public bool MoveNext()
{
// Note that this enumerator doesn't complain about the list
// changing during enumeration, but we do want to check that
// a change doesn't push us past the end of the list, rather
// than caching the size.
if(_idx >= _list.Count)
return false;
++_idx;
return true;
}
public void Reset()
{
_idx = -1;
}
public T Current
{
get
{
if(_idx < 0 || _idx >= _list.Count)
throw new InvalidOperationException();
return _list[_idx];
}
}
object IEnumerator.Current
{
get { return Current; }
}
public void Dispose()
{
}
public SnapshotableListEnumerator<T> Snapshot()
{
return new SnapshotableListEnumerator<T>(_list, _idx);
}
}
public static class SnapshotableListEnumeratorHelper
{
public static SnapshotableListEnumerator<T> GetSnapshotableEnumerator<T>(this IList<T> list)
{
return new SnapshotableListEnumerator<T>(list);
}
}
Now you can call GetSnapshotableEnumerator() on any implementation of IList<T> and use its Snapshot() method whenever you want a copy of the position within the enumeration.
Do you definitely need an IEnumerator instance? Why not enumerate using the index and store that in your own variable?
var list = new List<string>(new { "a", "b", "c" });
var pos = 2; // this is the position
richTextBoxOutput.AppendText(list[pos]);
You can reset at any time with:
pos = (desired position);
I have an object called Shape which contains a public int[,] coordinate { get; set; } field.
I have a separate class which has a collection of Shape objects. At a particular point, I wish to check:
if(shapes.Contains(shape))
{
// DoSomething
}
So in the Shape class I have added the IComparable reference and inserted the CompareTo method:
public int CompareTo(Shape other)
{
return this.coordinate.Equals(other.coordinate);
}
I am however getting an error:
Cannot implicitly convert type 'bool' to 'int'
How do I therefore phrase the return so that it returns an int and not a bool as it is doing so at the moment?
UPDATE
If I change the return code to:
return this.coordinate.CompareTo(other.coordinate);
I get the following error mesage:
Error 1 'ShapeD.Game_Objects.Shape' does not implement interface member 'System.IComparable.CompareTo(ShapeD.Game_Objects.Shape)'. 'ShapeD.Game_Objects.Shape.CompareTo(ShapeD.Game_Objects.Shape)' cannot implement 'System.IComparable.CompareTo(ShapeD.Game_Objects.Shape)' because it does not have the matching return type of 'int'. C:\Users\Usmaan\Documents\Visual Studio 2012\Projects\ShapeD\ShapeD\ShapeD\Game Objects\Shape.cs 10 18 ShapeD
IComparable implies, that two object can be compared in a sense, that you can tell which object has "higher value". It is generally used for sorting purposes. You should override Equals method instead .You should also use Point struct instead of array.
class Shape : IEquatable<Shape>
{
public Point coordinate { get; set; }
public bool Equals(Shape other)
{
if (other == null) return false;
return coordinate.Equals(other.coordinate);
}
public override bool Equals(object other)
{
if (other == null) return false;
if (ReferenceEquals(this, other)) return true;
var shape = other as Shape;
return Equals(shape);
}
public override int GetHashCode()
{
return coordinate.GetHashCode()
}
}
Since you only want to check for equality implement IEquatable interface not IComparable.
IComparable is used for sorting purpose
public bool Equals(Shape s)
{
int count=0;
int[] temp1=new int[this.coordinate.Length];
foreach(int x in this.coordinate)temp1[count++]=x;//convert to single dimention
count=0;
int[] temp2=new int[s.coordinate.Length];
foreach(int x in s.coordinate)temp2[count++]=x;//convert to single dimention
return temp1.SequenceEqual(temp2);//check if they are equal
}
NOTE
IEquatable should be implemented for any object that might be stored in a generic collection else you would have to also override Object's Equals method.Also as pointed out in other ans use Point struct instead of multidimentional array
For performing Contains check you need to override Equals operator in Shape class.
Resurrecting an old question only because it can still cause google hits despite some really poor answers.
You should not be using either CompareTo or Equals.
Neither of these fits with what you are trying to do and will only cause confusion, as evidenced by the answers written here.
Write your own method called something like IntersectsWith.
Have a look into any decent geometry library (e.g. boost if you're happy pulling from c++) as how to go about doing this.
As to casting from bool to int, this can be easily done by using the bool with the ? ternary operator.
I have a class which has two HashSet<String> collections as private members. Other classes in my code would like to be able to iterate over those HashSets and read their contents. I don't want to write a standard getter because another class could still do something like myClass.getHashSet().Clear(); Is there any other way to expose the elements of my HashSets to iteration without exposing the reference to the HashSet itself? I'd love to be able to do this in a way that is compatible with for-each loops.
Assuming you're using .NET 3.5, one alternative to writing the yield code yourself is to call a LINQ method. For example:
public IEnumerable<string> HashSet
{
get { return privateMember.Select(x => x); }
}
or
public IEnumerable<string> HashSet
{
get { return privateMember.Skip(0); }
}
There are various LINQ operators which could be used like this - using Skip(0) is probably the most efficient, as after the initial "skip 0 values" loop, it's probably just the foreach/yield return loop shown in the other answers. The Select version will call the no-op projection delegate for each item yielded. The chances of this difference being significant are astronomically small, however - I suggest you go with whatever makes the code clearest to you.
Expose a IEnumerable<T> property:
public IEnumerable<whatevertype> MyHashSet {
get {
return this.myHashSet;
}
}
Of course, the user of this code can cast that IEnumerable<T> to a HashSet<T> and edit elements, so to be on the safe side (while hurting performance), you can do:
public IEnumerable<whatevertype> MyHashSet {
get {
return this.myHashSet.ToArray();
}
}
or:
public IEnumerable<whatevertype> MyHashSet {
get {
foreach(var item in this.myHashSet) {
yield return item;
}
}
}
A more performant method of protection, but less convenient to the caller, is to return an IEnumerator<T>:
public IEnumerator<whatevertype> GetMyHashSetEnumerator() {
return this.myHashSet.GetEnumerator();
}
Add a method/property like this to avoid exposing the actual container:
public IEnumerable EnumerateFirst()
{
foreach( var item in hashSet )
yield return item;
}
You can also use the Select method to create a wrapper than can't be cast back to HashSet<T>:
public IEnumerable<int> Values
{
get { return _values.Select(value => value);
}
This avoids iterating over _values twice, as you would with .ToArray(), but keeps the implementation to a single clean line.
You may also provide a sequence like this:
public IEnumerable<string> GetHashSetOneValues()
{
foreach (string value in hashSetOne)
yield return value;
}
This method may then be called within a foreach loop:
foreach (string value in myObject.GetHashSetOneValues())
DoSomething(value);
This might be quite a bit too late to the party but the easiest way today would be to use Linq. Instead of writing
public IEnumerable<string> GetValues()
{
foreach(var elem in list)
yield return elem;
}
you can write
public IEnumerable<string> GetValues() => list;
Make your getter expose the HashSet as IEnumerable.
private HashSet<string> _mine;
public IEnumerable<string> Yours
{
get { return _mine; }
}
If the generic type is mutable, then that can still be modified, but no items can be added or removed from your HashSet.
Is there a common way to pass a single item of type T to a method which expects an IEnumerable<T> parameter? Language is C#, framework version 2.0.
Currently I am using a helper method (it's .Net 2.0, so I have a whole bunch of casting/projecting helper methods similar to LINQ), but this just seems silly:
public static class IEnumerableExt
{
// usage: IEnumerableExt.FromSingleItem(someObject);
public static IEnumerable<T> FromSingleItem<T>(T item)
{
yield return item;
}
}
Other way would of course be to create and populate a List<T> or an Array and pass it instead of IEnumerable<T>.
[Edit] As an extension method it might be named:
public static class IEnumerableExt
{
// usage: someObject.SingleItemAsEnumerable();
public static IEnumerable<T> SingleItemAsEnumerable<T>(this T item)
{
yield return item;
}
}
Am I missing something here?
[Edit2] We found someObject.Yield() (as #Peter suggested in the comments below) to be the best name for this extension method, mainly for brevity, so here it is along with the XML comment if anyone wants to grab it:
public static class IEnumerableExt
{
/// <summary>
/// Wraps this object instance into an IEnumerable<T>
/// consisting of a single item.
/// </summary>
/// <typeparam name="T"> Type of the object. </typeparam>
/// <param name="item"> The instance that will be wrapped. </param>
/// <returns> An IEnumerable<T> consisting of a single item. </returns>
public static IEnumerable<T> Yield<T>(this T item)
{
yield return item;
}
}
Well, if the method expects an IEnumerable you've got to pass something that is a list, even if it contains one element only.
passing
new[] { item }
as the argument should be enough I think
In C# 3.0 you can utilize the System.Linq.Enumerable class:
// using System.Linq
Enumerable.Repeat(item, 1);
This will create a new IEnumerable that only contains your item.
Your helper method is the cleanest way to do it, IMO. If you pass in a list or an array, then an unscrupulous piece of code could cast it and change the contents, leading to odd behaviour in some situations. You could use a read-only collection, but that's likely to involve even more wrapping. I think your solution is as neat as it gets.
In C# 3 (I know you said 2), you can write a generic extension method which might make the syntax a little more acceptable:
static class IEnumerableExtensions
{
public static IEnumerable<T> ToEnumerable<T>(this T item)
{
yield return item;
}
}
client code is then item.ToEnumerable().
This helper method works for item or many.
public static IEnumerable<T> ToEnumerable<T>(params T[] items)
{
return items;
}
I'm kind of surprised that no one suggested a new overload of the method with an argument of type T to simplify the client API.
public void DoSomething<T>(IEnumerable<T> list)
{
// Do Something
}
public void DoSomething<T>(T item)
{
DoSomething(new T[] { item });
}
Now your client code can just do this:
MyItem item = new MyItem();
Obj.DoSomething(item);
or with a list:
List<MyItem> itemList = new List<MyItem>();
Obj.DoSomething(itemList);
Either (as has previously been said)
MyMethodThatExpectsAnIEnumerable(new[] { myObject });
or
MyMethodThatExpectsAnIEnumerable(Enumerable.Repeat(myObject, 1));
As a side note, the last version can also be nice if you want an empty list of an anonymous object, e.g.
var x = MyMethodThatExpectsAnIEnumerable(Enumerable.Repeat(new { a = 0, b = "x" }, 0));
I agree with #EarthEngine's comments to the original post, which is that 'AsSingleton' is a better name. See this wikipedia entry. Then it follows from the definition of singleton that if a null value is passed as an argument that 'AsSingleton' should return an IEnumerable with a single null value instead of an empty IEnumerable which would settle the if (item == null) yield break; debate. I think the best solution is to have two methods: 'AsSingleton' and 'AsSingletonOrEmpty'; where, in the event that a null is passed as an argument, 'AsSingleton' will return a single null value and 'AsSingletonOrEmpty' will return an empty IEnumerable. Like this:
public static IEnumerable<T> AsSingletonOrEmpty<T>(this T source)
{
if (source == null)
{
yield break;
}
else
{
yield return source;
}
}
public static IEnumerable<T> AsSingleton<T>(this T source)
{
yield return source;
}
Then, these would, more or less, be analogous to the 'First' and 'FirstOrDefault' extension methods on IEnumerable which just feels right.
This is 30% faster than yield or Enumerable.Repeat when used in foreach due to this C# compiler optimization, and of the same performance in other cases.
public struct SingleSequence<T> : IEnumerable<T> {
public struct SingleEnumerator : IEnumerator<T> {
private readonly SingleSequence<T> _parent;
private bool _couldMove;
public SingleEnumerator(ref SingleSequence<T> parent) {
_parent = parent;
_couldMove = true;
}
public T Current => _parent._value;
object IEnumerator.Current => Current;
public void Dispose() { }
public bool MoveNext() {
if (!_couldMove) return false;
_couldMove = false;
return true;
}
public void Reset() {
_couldMove = true;
}
}
private readonly T _value;
public SingleSequence(T value) {
_value = value;
}
public IEnumerator<T> GetEnumerator() {
return new SingleEnumerator(ref this);
}
IEnumerator IEnumerable.GetEnumerator() {
return new SingleEnumerator(ref this);
}
}
in this test:
// Fastest among seqs, but still 30x times slower than direct sum
// 49 mops vs 37 mops for yield, or c.30% faster
[Test]
public void SingleSequenceStructForEach() {
var sw = new Stopwatch();
sw.Start();
long sum = 0;
for (var i = 0; i < 100000000; i++) {
foreach (var single in new SingleSequence<int>(i)) {
sum += single;
}
}
sw.Stop();
Console.WriteLine($"Elapsed {sw.ElapsedMilliseconds}");
Console.WriteLine($"Mops {100000.0 / sw.ElapsedMilliseconds * 1.0}");
}
As I have just found, and seen that user LukeH suggested too, a nice simple way of doing this is as follows:
public static void PerformAction(params YourType[] items)
{
// Forward call to IEnumerable overload
PerformAction(items.AsEnumerable());
}
public static void PerformAction(IEnumerable<YourType> items)
{
foreach (YourType item in items)
{
// Do stuff
}
}
This pattern will allow you to call the same functionality in a multitude of ways: a single item; multiple items (comma-separated); an array; a list; an enumeration, etc.
I'm not 100% sure on the efficiency of using the AsEnumerable method though, but it does work a treat.
Update: The AsEnumerable function looks pretty efficient! (reference)
Although it's overkill for one method, I believe some people may find the Interactive Extensions useful.
The Interactive Extensions (Ix) from Microsoft includes the following method.
public static IEnumerable<TResult> Return<TResult>(TResult value)
{
yield return value;
}
Which can be utilized like so:
var result = EnumerableEx.Return(0);
Ix adds new functionality not found in the original Linq extension methods, and is a direct result of creating the Reactive Extensions (Rx).
Think, Linq Extension Methods + Ix = Rx for IEnumerable.
You can find both Rx and Ix on CodePlex.
I recently asked the same thing on another post
Is there a way to call a C# method requiring an IEnumerable<T> with a single value? ...with benchmarking.
I wanted people stopping by here to see the brief benchmark comparison shown at that newer post for 4 of the approaches presented in these answers.
It seems that simply writing new[] { x } in the arguments to the method is the shortest and fastest solution.
This may not be any better but it's kind of cool:
Enumerable.Range(0, 1).Select(i => item);
Sometimes I do this, when I'm feeling impish:
"_".Select(_ => 3.14) // or whatever; any type is fine
This is the same thing with less shift key presses, heh:
from _ in "_" select 3.14
For a utility function I find this to be the least verbose, or at least more self-documenting than an array, although it'll let multiple values slide; as a plus it can be defined as a local function:
static IEnumerable<T> Enumerate (params T[] v) => v;
// usage:
IEnumerable<double> example = Enumerate(1.234);
Here are all of the other ways I was able to think of (runnable here):
using System;
using System.Collections.Generic;
using System.Linq;
public class Program {
public static IEnumerable<T> ToEnumerable1 <T> (T v) {
yield return v;
}
public static T[] ToEnumerable2 <T> (params T[] vs) => vs;
public static void Main () {
static IEnumerable<T> ToEnumerable3 <T> (params T[] v) => v;
p( new string[] { "three" } );
p( new List<string> { "three" } );
p( ToEnumerable1("three") ); // our utility function (yield return)
p( ToEnumerable2("three") ); // our utility function (params)
p( ToEnumerable3("three") ); // our local utility function (params)
p( Enumerable.Empty<string>().Append("three") );
p( Enumerable.Empty<string>().DefaultIfEmpty("three") );
p( Enumerable.Empty<string>().Prepend("three") );
p( Enumerable.Range(3, 1) ); // only for int
p( Enumerable.Range(0, 1).Select(_ => "three") );
p( Enumerable.Repeat("three", 1) );
p( "_".Select(_ => "three") ); // doesn't have to be "_"; just any one character
p( "_".Select(_ => 3.3333) );
p( from _ in "_" select 3.0f );
p( "a" ); // only for char
// these weren't available for me to test (might not even be valid):
// new Microsoft.Extensions.Primitives.StringValues("three")
}
static void p <T> (IEnumerable<T> e) =>
Console.WriteLine(string.Join(' ', e.Select((v, k) => $"[{k}]={v,-8}:{v.GetType()}").DefaultIfEmpty("<empty>")));
}
For those wondering about performance, while #mattica has provided some benchmarking information in a similar question referenced above, My benchmark tests, however, have provided a different result.
In .NET 7, yield return value is ~9% faster than new T[] { value } and allocates 75% the amount of memory. In most cases, this is already hyper-performant and is as good as you'll ever need.
I was curious if a custom single collection implementation would be faster or more lightweight. It turns out because yield return is implemented as IEnumerator<T> and IEnumerable<T>, the only way to beat it in terms of allocation is to do that in my implementation as well.
If you're passing IEnumerable<> to an outside library, I would strongly recommend not doing this unless you're very familiar with what you're building. That being said, I made a very simple (not-reuse-safe) implementation which was able to beat the yield method by 5ns and allocated only half as much as the array.
Because all tests were passed an IEnumerable<T>, value types generally performed worse than reference types. The best implementation I had was actually the simplest - you can look at the SingleCollection class in the gist I linked to. (This was 2ns faster than yield return, but allocated 88% of what the array would, compared to the 75% allocated for yield return.)
TL:DR; if you care about speed, use yield return item. If you really care about speed, use a SingleCollection.
The easiest way I'd say would be new T[]{item};; there's no syntax to do this. The closest equivalent that I can think of is the params keyword, but of course that requires you to have access to the method definition and is only usable with arrays.
Enumerable.Range(1,1).Select(_ => {
//Do some stuff... side effects...
return item;
});
The above code is useful when using like
var existingOrNewObject = MyData.Where(myCondition)
.Concat(Enumerable.Range(1,1).Select(_ => {
//Create my object...
return item;
})).Take(1).First();
In the above code snippet there is no empty/null check, and it is guaranteed to have only one object returned without afraid of exceptions. Furthermore, because it is lazy, the closure will not be executed until it is proved there is no existing data fits the criteria.
To be filed under "Not necessarily a good solution, but still...a solution" or "Stupid LINQ tricks", you could combine Enumerable.Empty<>() with Enumerable.Append<>()...
IEnumerable<string> singleElementEnumerable = Enumerable.Empty<string>().Append("Hello, World!");
...or Enumerable.Prepend<>()...
IEnumerable<string> singleElementEnumerable = Enumerable.Empty<string>().Prepend("Hello, World!");
The latter two methods are available since .NET Framework 4.7.1 and .NET Core 1.0.
This is a workable solution if one were really intent on using existing methods instead of writing their own, though I'm undecided if this is more or less clear than the Enumerable.Repeat<>() solution. This is definitely longer code (partly due to type parameter inference not being possible for Empty<>()) and creates twice as many enumerator objects, however.
Rounding out this "Did you know these methods exist?" answer, Array.Empty<>() could be substituted for Enumerable.Empty<>(), but it's hard to argue that makes the situation...better.
I'm a bit late to the party but I'll share my way anyway.
My problem was that I wanted to bind the ItemSource or a WPF TreeView to a single object. The hierarchy looks like this:
Project > Plot(s) > Room(s)
There was always going to be only one Project but I still wanted to Show the project in the Tree, without having to pass a Collection with only that one object in it like some suggested.
Since you can only pass IEnumerable objects as ItemSource I decided to make my class IEnumerable:
public class ProjectClass : IEnumerable<ProjectClass>
{
private readonly SingleItemEnumerator<AufmassProjekt> enumerator;
...
public IEnumerator<ProjectClass > GetEnumerator() => this.enumerator;
IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
}
And create my own Enumerator accordingly:
public class SingleItemEnumerator : IEnumerator
{
private bool hasMovedOnce;
public SingleItemEnumerator(object current)
{
this.Current = current;
}
public bool MoveNext()
{
if (this.hasMovedOnce) return false;
this.hasMovedOnce = true;
return true;
}
public void Reset()
{ }
public object Current { get; }
}
public class SingleItemEnumerator<T> : IEnumerator<T>
{
private bool hasMovedOnce;
public SingleItemEnumerator(T current)
{
this.Current = current;
}
public void Dispose() => (this.Current as IDisposable).Dispose();
public bool MoveNext()
{
if (this.hasMovedOnce) return false;
this.hasMovedOnce = true;
return true;
}
public void Reset()
{ }
public T Current { get; }
object IEnumerator.Current => this.Current;
}
This is probably not the "cleanest" solution but it worked for me.
EDIT
To uphold the single responsibility principle as #Groo pointed out I created a new wrapper class:
public class SingleItemWrapper : IEnumerable
{
private readonly SingleItemEnumerator enumerator;
public SingleItemWrapper(object item)
{
this.enumerator = new SingleItemEnumerator(item);
}
public object Item => this.enumerator.Current;
public IEnumerator GetEnumerator() => this.enumerator;
}
public class SingleItemWrapper<T> : IEnumerable<T>
{
private readonly SingleItemEnumerator<T> enumerator;
public SingleItemWrapper(T item)
{
this.enumerator = new SingleItemEnumerator<T>(item);
}
public T Item => this.enumerator.Current;
public IEnumerator<T> GetEnumerator() => this.enumerator;
IEnumerator IEnumerable.GetEnumerator() => this.GetEnumerator();
}
Which I used like this
TreeView.ItemSource = new SingleItemWrapper(itemToWrap);
EDIT 2
I corrected a mistake with the MoveNext() method.
I prefer
public static IEnumerable<T> Collect<T>(this T item, params T[] otherItems)
{
yield return item;
foreach (var otherItem in otherItems)
{
yield return otherItem;
}
}
This lets you call item.Collect() if you want the singleton, but it also lets you call item.Collect(item2, item3) if you want