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Why does IEnumerator<T> inherit from IDisposable while the non-generic IEnumerator does not?
(6 answers)
Do I need to consider disposing of any IEnumerable<T> I use?
(1 answer)
Closed 1 year ago.
According to the accepted answer to Enumerator disposal when not using using, foreach or manually calling Dispose() enumerators in C# must be disposed when finished with, whether you let foreach do this automatically, or do it yourself if you prefer to write out the equivalent logic by hand.
I wasn't expecting this; would have thought enumerators would be handled by the garbage collector. I'm guessing it's along the lines of:
Database queries are also enumerable, and those need to be disposed because they could be holding database connections, which are a scarcer resource than memory.
To correctly handle this case, the framework designers decided to just make enumerators implement IDisposable, so the contract is they should always be disposed; for in-memory collections like strings, arrays and lists, this will be a no-op, but it makes the overall design simpler than trying to make some kinds of enumerators implement a different interface.
Is this correct, or am I missing something?
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Can anyone explain IEnumerable and IEnumerator to me? [closed]
(16 answers)
Closed 7 days ago.
I want to know the exact place where we should use IEnumberable<T>
I know how IEnumerable<T> work and returns IEnumerator<T> and all that but the ultimate goal of IEnumerable<T> is to query the data from the collection isn't it? That is what we can already do using foreach() loop ? So when to use IEnumerable<T>? what is the actual practical scenario where the IEnumerable<T> is the only option to query the collection?
but the ultimate goal of IEnumerable<T> is to query the data from the collection isn't it?
No; the goal of IEnumerable<T> is to provide access to a sequence, which may or may not be a collection. The point being to abstract away what the underlying source is. It could be a raw collection, but it could be:
some LINQ (or similar) projection (collection.Where(...).Select(...) etc)
an open query to ADO.NET, redis, a socket, gRPC, a file or some other data provider that isn't readily countable, repeatable, etc - just: "a sequence"
an in-process data generator
some producer/consumer setup
etc
If you know you're always iterating a collection, then sure: feel free to use the concrete type, or ICollection<T>/IList<T> etc; but: not every sequence is a collection.
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what is relation between GC, Finalize() and Dispose?
(3 answers)
Does C# app exit automatically dispose managed resources?
(4 answers)
What are the uses of "using" in C#?
(29 answers)
Closed 2 years ago.
I got stuck in the weeds of how IDisposable and the GarbageCollector work.
Suppose you have an IDisposable object, which doesn't actually have an resources that it's holding onto (but the Dispose() method is going to do something when called). And suppose you declare it in the head of a using block, but don't actually interact with the object over the course of the block.
What guarantees do I have about how GarbageCollection will operate?
i.e.
using(new MyConceptuallyDisposableObject())
{
DoSomeWork();
await DoSomeAsyncWork();
}//PointX
Note that:
MyConceptuallyDisposableObject doesn't declare a finaliser / destructor.
(Assume that developers will never forget to using`.Dispose()` my object)
MyConceptuallyDisposableObject doesn't call GC.SuppressFinalise(this) anywhere.
Am I guaranteed that the object that I constructed will:
Will not have .Dispose() called on it before PointX?
Will have .Dispose() called on it at exactly PointX?
Will not get GarbageCollected/Finalised at any point before PointX?
Will not get GarbageCollected/Finalised before it has had .Dispose() called on it?
Suppose I then change my code to make MyConceptuallyDisposableObject call GC.SuppressFinalise(this) in its constructor. (Bearing in mind that there isn't any Destructor or Finaliser)
Does that change any of the answers to the specific questions above?
Does anything change in general, then?
Does it mean that the GC never cleans up my object at all and I'll end up with a memory leak?
*Context:*
Posted for those who are inevitably curious, but PLEASE don't answer based suggesting other ways to achieve this or that I shouldn't do this. Right now, I'm much more invested in understanding the guts of the above concepts in their abstract sense, not discussing whether my initial attempt was sensible.
I want to write a DisposableAction() class, which accepts 2 Actions. One to perform when you construct it, and one to perform when you Dispose() it.
I thought I knew all the answers to the above (and that they were "Yes", "Yes", "Yes", "Yes", "No", "Almost nothing unless you're incredibly perf-sensitive", and "No".), but I've been trying to diagnose a bug which appears to contradict these beliefs.
IDisposable and garbage collection are unrelated, except for the one situation where an object implements a finalizer that happens to call .Dispose().
Unless you know for sure, 100%, and explicitly, that an object has a finalizer that calls .Dispose() then you must call .Dispose() explicitly (or with a using) to ensure the object is disposed.
The answers to your questions:
Yes.
Yes.
Yes.
Yes.
No.
No.
No.
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How to tell if an IEnumerable<T> is subject to deferred execution?
(6 answers)
Closed 9 years ago.
I have a Cache wrapper class that I use, which provides type safety and segmenting and other nice things.
I want to make it prevent me from shooting myself in the foot by caching an un-materialized LINQ query and only accept lists/collections...
Is there a way to detect if an IEnumerable is a LINQ query?
Maybe I'm answering my own question and should throw an exception when T is IEnumerable but not ICollection.
I would suggest just wrapping the IEnumerable<T> within your own collection, "materializing" it yourself.
This will provide full safety and more consistency, at the expense of potentially generating another collection instance and copying the references over.
You could always do a check for ICollection<T> and not regenerate, or similar, but there are still advantages to copying the contents into your own list. One major one is that you then control the one and only instance of the collection - you don't have to worry about another object adding or removing items (which may or may not be an issue, but is likely problematic for segmenting).
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Closed 10 years ago.
I am currently learning C# and I have a situation where I have a class that contains a ISet. I don't wish clients to modify this set directly, and most clients only Add and Remove, and I provide accessors through my class to do this.
However, I have one client that wishes to know more about this set and its contents. I don't really want to muddy the wrapper class itself with lots of methods for this one client, so I would prefer to be able to return the set itself in a immutable way.
I found I can't - well, not really. The only options I seem to have are:
Return an IEnumerable (No: restrictive functionality);
ReadOnlyCollection (No: It's a LIST);
Return a copy (No: Bad form IMHO, allows clients to modify the returned collection perhaps unaware that it's not going to change the real object, plus it has performance overhead);
Implement my own ReadOnlySet (No: Would need to derive from ISet and thus meaning I need to implement mutators, probably firing exceptions, I would rather compile time errors - not runtime).
Am I missing something? Am I being unreasonable? Is my only option to provide the full set of accessors on my wrapper? Am I incorrect in my original intent to keep the wrapper clean for the vast majority of clients?
So two questions:
Why isn't there an standard C# immutable Collection interface? It seems like a fairly reasonable requirement?
Why is ReadOnlyCollection annoyingly called ReadOnlyCollection when it is really a ReadOnlyList? I was going to bite the bullet and use that until I found out it was a List (and I use a Set).
Why isn't there a standard C# immutable interface? It seems like a
fairly reasonable requirement?
A standard C# immutable¹ interface already exists: it's called IEnumerable and all containers implement it.
More powerful immutable interfaces are problematic, because there are many kinds of immutability. If the BCL team decided to pick one definition of immutability and elevate it to the immutability status it's certain that down the road people looking for a different kind of immutability would complain about the choice.
Satisfying everyone would mean not only sorting all of the immutability mess out but creating lots of interfaces (good luck picking good names for them too) and baking all these immutability concepts into the language well enough to make immutability a first-class citizen -- remember that there are no second chances here, once you ship a public class its public interface is immutable forever (pun intended). While all of this might be good to have, I 'm really skeptical about the cost/benefit ratio.
It's not difficult to define IReadOnlyList, IReadOnlySet and such if you do require them. I assume that they do not already exist because again, minus 100 points.
ReadOnlyCollection is IMHO either a concession or a class that was required internally for the BCL and exposed to the world because hey, free functionality at really low cost for the BCL team (since it would have to be implemented, documented and tested anyway). In any case I don't think that it does not live in the glamorous System.Collections.Generic neighborhood by chance.
Why is ReadOnlyCollection annoyingly called ReadOnlyCollection when it
is really a ReadOnlyList? I was going to bite the bullet and use that
until I found out it was a List (and I use a Set).
I 'm sure the BCL team would love to be able to go back in time and fix that, because it's almost certainly one of those little inconsistencies that unavoidably sneak into any library of comparable scope. Since ReadOnlyCollection implements IList it should definitely have been called ReadOnlyList.
However, given that a "list" offers more functionality than a "collection", I don't see how this would stop you. Neither is a Set, so you would have to build set-related functionality on top of them in any case (which is not a good idea; just build read-only semantics on top of Set).
¹ We 're tossing around "immutable" a lot here, but that word does not have a singular meaning. I think it would be more appropriate to use "read-only", but I 'll go with your choice of word for consistency.
This may help,
http://blogs.msdn.com/b/jaredpar/archive/2008/04/22/api-design-readonlycollection-t.aspx
I think the only way for you to provide a read-only 'copy' of the set without actually copying the data into another instance of the same or a different structure, is to go with the wrapper and implement all the item-adding-and-removing methods to throw an exception.
If your set is exposed only as an ISet anyway, consumers are only going to see the members defined on the interface, no matter what your wrapper contains - that doesn't seem like it's a bad thing.
I agree it would be nice if there were better support in .net for both immutability and read-only wrappers, though I think it's important to note that there is a huge difference between the concepts. A read-only wrapper promises its creator that consumers of it won't be able to change the underlying object, but makes no promise to consumers that the underlying object itself won't change. By contrast, an immutable object promises its creator and consumers that its values won't change.
I'm not sure why the notion that there are many different types of immunity should be a problem. If I have a generic ImmutableList<T> which takes an unqualified T my expectation would be that it will always contain the same T's as it did when it was created. The collection could in no way affect whether any of the properties of the T's could change, and thus it shouldn't be expected to.
If I had my druthers, most of the collection-related interfaces would include readable, mutable, and immutable variants (mutable and immutable would both extend from readable). I'd also add a write-only contravariant IAppendable interface, as well as an IImmutableEnumerable derived from IEnumerable (I'd add a ToImmutable method to IEnumerable (and IImmutableEnumerable); an implementation could construct an immutable collection, but in some cases that might not be the best approach. For example, a mutable object might implement IEnumerable by return a mutable number of copies of a mutable element. If the number of copies is large, converting to a simple collection could be very wasteful.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Proper use of the IDisposable interface
When is Dispose necessary?
If I write a class, which uses graphics, or threads for example, must I implement the IDisposable interface to write a Dispose() method or else memory leak occurs?
Does Dipose() run when the GC reaches it?
If I implement a Dispose() method, shall I call Dispose() on all the disposable fields in the class when "disposing" parameter is true, or is it automatic?
What is "unmanaged resource"?
So I'm pretty unsure about it, I'd appreciate anything that helps me understand these things :)
Thank You
IDisposable is just a pattern to follow. It doesn't do anything, in and of itself, special (other than fitting the requirements of the using statement).
If you're working with a native resource, the resource isn't "known" to the garbage collector. IDisposable is the convention used to allow you to free this resource deterministically.
For details, I wrote a detailed series on IDisposable which talks about why and how to implement it for various scenarios (including wrapping a native resource, encapsulating other IDispsable types, etc).