Is it possible to implement an infinite IEnumerable without using yield with only C# code?

Posted by sinelaw on Stack Overflow See other posts from Stack Overflow or by sinelaw
Published on 2013-11-07T03:27:33Z Indexed on 2013/11/07 3:54 UTC
Read the original article Hit count: 367

Filed under:

c#

|

ienumerable

|

infinite-loop

Edit: Apparently off topic...moving to Programmers.StackExchange.com.

This isn't a practical problem, it's more of a riddle.

Problem

I'm curious to know if there's a way to implement something equivalent to the following, but without using yield:

IEnumerable<T> Infinite<T>()
{
    while (true) { yield return default(T); }
}

Rules

You can't use the yield keyword
Use only C# itself directly - no IL code, no constructing dynamic assemblies etc.
You can only use the basic .NET lib (only mscorlib.dll, System.Core.dll? not sure what else to include). However if you find a solution with some of the other .NET assemblies (WPF?!), I'm also interested.
Don't implement IEnumerable or IEnumerator.

Notes

The closest I've come yet:

IEnumerable<int> infinite = null;
infinite = new int[1].SelectMany(x => new int[1].Concat(infinite));

This is "correct" but hits a StackOverflowException after 14399 iterations through the enumerable (not quite infinite).

I'm thinking there might be no way to do this due to the CLR's lack of tail recursion optimization. A proof would be nice :)

© Stack Overflow or respective owner

Is it possible to implement an infinite IEnumerable without using yield with only C# code?

Posted by sinelaw on Programmers See other posts from Programmers or by sinelaw
Published on 2013-11-07T03:48:05Z Indexed on 2013/11/07 4:12 UTC
Read the original article Hit count: 367

Filed under:

c#

|

LINQ

|

clr

This isn't a practical problem, it's more of a riddle.

Problem

I'm curious to know if there's a way to implement something equivalent to the following, but without using yield:

IEnumerable<T> Infinite<T>()
{
    while (true) { yield return default(T); }
}

Rules

You can't use the yield keyword
Use only C# itself directly - no IL code, no constructing dynamic assemblies etc.
You can only use the basic .NET lib (only mscorlib.dll, System.Core.dll? not sure what else to include). However if you find a solution with some of the other .NET assemblies (WPF?!), I'm also interested.
Don't implement IEnumerable or IEnumerator.

Notes

The closest I've come yet:

IEnumerable<int> infinite = null;
infinite = new int[1].SelectMany(x => new int[1].Concat(infinite));

This is "correct" but hits a StackOverflowException after 14399 iterations through the enumerable (not quite infinite).

I'm thinking there might be no way to do this due to the CLR's lack of tail recursion optimization. A proof would be nice :)

© Programmers or respective owner

Related posts about c#

.NET WebRequest.PreAuthenticate not quite what it sounds like

as seen on West-Wind - Search for 'West-Wind'
I’ve run into the problem a few times now: How to pre-authenticate .NET WebRequest calls doing an HTTP call to the server – essentially send authentication credentials on the very first request instead of waiting for a server challenge first? At first glance this sound like it should be easy:… >>> More
HttpWebRequest and Ignoring SSL Certificate Errors

as seen on West-Wind - Search for 'West-Wind'
Man I can't believe this. I'm still mucking around with OFX servers and it drives me absolutely crazy how some these servers are just so unbelievably misconfigured. I've recently hit three different 3 major brokerages which fail HTTP validation with bad or corrupt certificates at least according to… >>> More
The dynamic Type in C# Simplifies COM Member Access from Visual FoxPro

as seen on West-Wind - Search for 'West-Wind'
I’ve written quite a bit about Visual FoxPro interoperating with .NET in the past both for ASP.NET interacting with Visual FoxPro COM objects as well as Visual FoxPro calling into .NET code via COM Interop. COM Interop with Visual FoxPro has a number of problems but one of them at least got a lot… >>> More
Dynamic Type to do away with Reflection

as seen on West-Wind - Search for 'West-Wind'
The dynamic type in C# 4.0 is a welcome addition to the language. One thing I’ve been doing a lot with it is to remove explicit Reflection code that’s often necessary when you ‘dynamically’ need to walk and object hierarchy. In the past I’ve had a number of ReflectionUtils that used string based expressions… >>> More
Finding a Relative Path in .NET

as seen on West-Wind - Search for 'West-Wind'
Here’s a nice and simple path utility that I’ve needed in a number of applications: I need to find a relative path based on a base path. So if I’m working in a folder called c:\temp\templates\ and I want to find a relative path for c:\temp\templates\subdir\test.txt I want to receive back subdir\test… >>> More

Related posts about ienumerable

Grouping consecutive identical items: IEnumerable<T> to IEnumerable<IEnumerable<T>>

as seen on Stack Overflow - Search for 'Stack Overflow'
I've got an interresting problem: Given an IEnumerable<string>, is it possible to yield a sequence of IEnumerable<string> that groups identical adjacent strings in one pass? Let me explain. Considering the following IEnumerable<string> (pseudo representation): {"a","b","b","b"… >>> More
IEnumerable<IEnumerable<T>> to IEnumerable<T> using LINQ

as seen on Stack Overflow - Search for 'Stack Overflow'
How to split an IEnumerable of IEnumerables to one flat IEnumerable using LINQ (or someway else)? >>> More
IEnumerable.GetEnumerator() and IEnumerable<T>.GetEnumerator()

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, In the .net framework, there's a generic IEnumerable<T> interface which inherits from the not-generic IEnumerable, and they both have a GetEnumerator() method. The only differents between these two GetEnumerator() is the return type. Now I have a similar design, but when I compile the… >>> More
Create a Generic IEnumerable<T> given a IEnumerable and the member datatypes

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I get an IEnumerable which I know is a object array. I also know the datatype of the elements. Now I need to cast this to an IEnumerable<T, where T is a supplied type. For instance IEnumerable results = GetUsers(); IEnumerable<T> users = ConvertToTypedIEnumerable(results, typeof(User)); I… >>> More
Casting from IEnumerable<Object> to IEnumerable<string>

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi All, Recently I found a very surprising behavior in c#. I had a method which takes IEnumerable<Object> as a parameter and i was passing IEnumerable<string> but it's not possible. While in c# everything can be upcast to Object than why this is not possible? It's totally confusing for… >>> More