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How can I test that LINQ Range operator is deferred?

I have implemented some sort of LINQ Range operator and do want to have a test which will verify that the Range operator is actually deferred.
My Range operator methods:
/// <summary>
/// The Range static method, validation part.
/// </summary>
/// <param name="start">The start.</param>
/// <param name="count">The count.</param>
/// <returns></returns>
public static IEnumerable<int> Range(int start, int count)
{
long max = ((long) start) + count - 1;
if (count < 0 || max > Int32.MaxValue) throw new ArgumentOutOfRangeException(nameof(count));
return RangeIterator(start, count);
}
/// <summary>
/// The Range operator iterator.
/// </summary>
/// <param name="start">The start.</param>
/// <param name="count">The count.</param>
/// <returns></returns>
static IEnumerable<int> RangeIterator(int start, int count)
{
for (int i = 0; i < count; ++i)
{
yield return start + i;
}
}
For the other deferred operators I have created ThrowingExceptionEnumerable utility class, which helps with testing:
/// <summary>
/// The class responsible for verifying that linq operator is deferred.
/// </summary>
/// <typeparam name="T"></typeparam>
public sealed class ThrowingExceptionEnumerable<T> : IEnumerable<T>
{
/// <summary>
/// The methods throws <see cref="InvalidOperationException"/>.
/// </summary>
/// <returns></returns>
public IEnumerator<T> GetEnumerator()
{
throw new InvalidOperationException();
}
/// <inheritdoc />
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
/// <summary>
/// The method which checks that the given <see cref="deferredFunction"/> actually uses deferred execution.
/// When the function just call itself it should not throw an exception. But, when using the result
/// by calling <see cref="GetEnumerator"/> and than GetNext() methods should throws the <see cref="InvalidOperationException"/>.
/// </summary>
/// <typeparam name="TSource">The deferred function source type.</typeparam>
/// <typeparam name="TResult">The deferred function result type.</typeparam>
/// <param name="deferredFunction">The deferred function (unit of work under the test).</param>
public static void AssertDeferred<TSource,TResult>(
Func<IEnumerable<TSource>, IEnumerable<TResult>> deferredFunction)
{
var source = new ThrowingExceptionEnumerable<TSource>();
// Does not throw any exception here, because GetEnumerator() method is not yet used.
var result = deferredFunction(source);
// Does not throw InvalidOperationException even here, despite the fact that we retrieve the enumerator.
using var iterator = result.GetEnumerator();
Assert.Throws<InvalidOperationException>(() => iterator.MoveNext());
}
And for instance deferred Select operator has the following test:
/// <summary>
/// Should check that Select operator is deferred.
/// </summary>
[Fact]
public void VerifySelectExecutionIsDeferred()
{
ThrowingExceptionEnumerable<int>.AssertDeferred<int, int>(source => source.Select(x => x));
}
The first problem I have faced during writing such unit test for the Range operator is that Range is actually a static method and not an extension method. Also the thing is, that Range signature does not have a source parameter, so the same approach can not be used.
Do you have some clever ideas, how it can be tested?

External code isn't going to be able to do anything to verify that the values are generated on the fly. The only actual difference between a method like this and one that materializes a collection and returns it is the memory footprint at scale, which is quite difficult to reliably test in a unit test.
You can clearly tell that it doesn't do that my looking at the code, but you'd need to alter the implementation in some pretty significant way to end up with something that would allow you to verify that in a unit test (such as writing a more generalized "Generate" method that used a delegate to generate the next value).
If you had some sort of hard requirement that your implementation has unit tests to verify such things, I'd write such a Generate method, implement your Range method by calling Generate, write a unit test to verify that Generate doesn't call the delegate until generating the next value in the sequence, and then assert that the Range method defers execution because it uses Generate to produce its sequence. I wouldn't want to do this in production code though, this would really be just a way of meeting the requirement and making some sacrifices in readability and (mild) performance for the sake of it.

Default value for flags enum in a RESTful WCF service

WCF supports using enum types that are tagged with the FlagsAttribute as parameters within an UriTemplate. Like this:
[DataContract]
[Flags]
public enum OptionsEnum
{
[EnumMember]
None = 0,
[EnumMember]
MyOption1 = 1,
[EnumMember]
MyOption2 = 2,
[EnumMember]
MyOption3 = 4,
[EnumMember]
MyOption4 = 8
}
[ServiceContract]
public interface MyServiceContract
{
[OperationContract]
[WebInvoke(Method = "GET", UriTemplate = "resource?options={options}")]
void MyOperation(OptionsEnum options);
}
The resource can then be requested via URLs like this:
GET /resource?options=None
GET /resource?options=MyOption1
GET /resource?options=MyOption1,MyOption3
All of this works really nicely as long the URL actually contains a value for the options parameter. However, if I request the resource without specifying a value in the URL, like this:
GET /resource
I get an exception with the message Value cannot be null.\r\nParameter name: value
and the following stack trace:
at System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult)
at System.Enum.Parse(Type enumType, String value, Boolean ignoreCase)
at System.ServiceModel.Dispatcher.QueryStringConverter.ConvertStringToValue(String parameter, Type parameterType)
at System.ServiceModel.Dispatcher.UriTemplateDispatchFormatter.DeserializeRequest(Message message, Object[] parameters)
at System.ServiceModel.Dispatcher.DispatchOperationRuntime.DeserializeInputs(MessageRpc& rpc)
at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc)
at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)
at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc)
at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)
Obviously, this is because QueryStringConverter passes null into Enum.Parse(...) in this case. As a result the implementation of MyServiceContract will not be executed.
Of course I could just switch to string for the type of the options parameter and do all the parsing stuff myself within the service implementation, but that's not what I want, really.
Does anyone know a clean solution to have OptionsEnum.None passed into the service implementation if the URL does not contain a value (just like 0 is passed for omitted parameters of type int)?
I already tried using a custom TypeConverter implementation, but even that does not seem to work. Looking at the implementation of QueryStringConverter it seems like it will always try to convert enum types by itself.

Ok, I have found a solution that is reusable and does not involve switching to string for the type of the flags parameter. I was hoping for something simpler, though. Anyway, in case it helps someone else, here it is.
The approach is relatively simple:
Wrap the enum in a reference type.
Use a TypeConverter to customize the process of converting the value from string to our flags enum as implemented by WCF's QueryStringConverter.
/// <summary>
/// Wraps a flags enum value.
/// </summary>
/// <remarks>
/// This class is meant to be used in conjunction with
/// <see cref="FlagsConverter{TFlags,TEnum}"/> and simply boxes an enum.
/// This is necessary in order to customize WCF's default behavior for enum
/// types (as implemented by <see cref="QueryStringConverter"/>) by using a
/// <see cref="TypeConverter"/>.
/// </remarks>
/// <devdoc>
/// We prefer this over using an 1-Tuple (<see cref="Tuple{T1} "/>) as it
/// allows us to add constraints on the type parameter. Also, the value
/// wrapped by a <see cref="Tuple{T1} "/> is read-only, which we don't want
/// here, as there is no reason to prevent [OperationContract] methods from
/// writing the wrapped <see cref="Value"/>.
/// </devdoc>
/// <typeparam name="TEnum">
/// The enum type. Must be attributed with <see cref="FlagsAttribute"/>.
/// </typeparam>
public abstract class Flags<TEnum>
where TEnum : struct, IConvertible
{
// Use a static c'tor to add run-time checks on the type parameter that
// cannot be checked at compile-time via constraints.
static Flags()
{
if (!typeof(TEnum).IsEnum)
{
throw new InvalidOperationException("T is not an enum");
}
if (!typeof(TEnum).IsDefined(typeof(FlagsAttribute), false))
{
throw new InvalidOperationException("T is not a flags enum");
}
}
/// <summary>
/// The enum value.
/// </summary>
public TEnum Value
{
get;
set;
}
}
/// <summary>
/// A <see cref="TypeConverter"/> implementation that converts from
/// <c>string</c> to <see cref="Flags{TEnum}"/>.
/// </summary>
/// <remarks>
/// <para>
/// Meant to be used in conjunction with <see cref="Flags{TEnum}"/>.
/// The purpose of this <see cref="TypeConverter"/> implementation is to
/// convert both <c>null</c> and the empty string to <c>default(TEnum)</c>
/// instead of throwing an exception. This way, a flags enum (wrapped in an
/// instance of <see cref="Flags{TEnum}"/>) can be used as the type of an
/// optional parameter in a RESTful WCF <c>OperationContract</c> method.
/// </para>
/// <para>
/// If the string value (as provided by <see cref="QueryStringConverter"/>)
/// is <c>null</c> or empty or can be successfully parsed into an enum
/// value of type <typeparamref name="TEnum"/>, this implementation will
/// provide an instance of <typeparamref name="TFlags"/>. Thus, there is no
/// need to check a <typeparamref name="TFlags"/>-typed value for
/// <c>null</c> within the implementation of an <c>OperationContract</c>
/// method.
/// </para>
/// </remarks>
/// <typeparam name="TFlags">
/// A sub-class of <see cref="Flags{TEnum}"/>. Must have a default c'tor.
/// </typeparam>
/// <typeparam name="TEnum">
/// The enum type. Must be attributed with <see cref="FlagsAttribute"/>.
/// </typeparam>
public class FlagsConverter<TFlags, TEnum> : TypeConverter
where TFlags : Flags<TEnum>, new()
where TEnum : struct, IConvertible
{
public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
{
return sourceType == typeof(string);
}
public override object ConvertFrom(ITypeDescriptorContext context,
CultureInfo culture, object value)
{
if (string.IsNullOrEmpty((string)value))
{
// The following line is what Flags<> and FlagsConverter<,> is
// all about: Provide the enum's default value (meaning no flag
// is set) for null and the empty string instead of passing it
// into Enum.Parse() (which results in an ArgumentException).
return new TFlags { Value = default(TEnum) };
}
// Otherwise, just pass the value on the Enum.Parse(), i.e. don't
// add any further changes to WCF's default behavior as implemented
// by QueryStringConverter.
return new TFlags { Value = (TEnum)Enum.Parse(typeof(TEnum), (string)value, true) };
}
}
These two classes can now be used to solve the problem like this
(reusing the example from the original question):
[DataContract]
[Flags]
public enum OptionsEnum
{
[EnumMember]
None = 0,
[EnumMember]
MyOption1 = 1,
[EnumMember]
MyOption2 = 2,
[EnumMember]
MyOption3 = 4,
[EnumMember]
MyOption4 = 8
}
[DataContract]
[TypeConverter(typeof(FlagsConverter<MyOptionalFlags, OptionsEnum>))]
public class MyOptionalFlags
: Flags<OptionsEnum>
{
// We don't add anything here, as the whole purpose of this class is to
// wrap the OptionsEnum in a class that will be instantiated by the
// attributed FlagsConverter.
}
[ServiceContract]
public interface MyServiceContract
{
[OperationContract]
[WebInvoke(Method = "GET", UriTemplate = "resource?options={options}")]
void MyOperation(MyOptionalFlags options);
}
public class MyServiceContractImpl
: MyServiceContract
{
public void MyOperation(MyOptionalFlags options)
{
if (options.Value == OptionsEnum.None)
{
// We will now get here for requests that do not specify a
// value for the options parameter in the URL. Note that just
// like for an enum value, we don't have to check if options is
// null here.
}
}
}

IEnumerable Concat Missing, does not contain a definition for 'Concat'

I have the following Class which inherits IEnumerable
public class LinesEnumerable : IEnumerable<Point>
{
protected readonly IPointSeries _pointSeries;
protected readonly ICoordinateCalculator<double> _xCoordinateCalculator;
protected readonly ICoordinateCalculator<double> _yCoordinateCalculator;
protected readonly bool _isDigitalLine;
/// <summary>
/// Initializes a new instance of the <see cref="LinesEnumerable" /> class.
/// </summary>
/// <param name="pointSeries">The point series.</param>
/// <param name="xCoordinateCalculator">The x coordinate calculator.</param>
/// <param name="yCoordinateCalculator">The y coordinate calculator.</param>
/// <param name="isDigitalLine">if set to <c>true</c> return a digital line .</param>
public LinesEnumerable(IPointSeries pointSeries, ICoordinateCalculator<double> xCoordinateCalculator, ICoordinateCalculator<double> yCoordinateCalculator, bool isDigitalLine)
{
_pointSeries = pointSeries;
_xCoordinateCalculator = xCoordinateCalculator;
_yCoordinateCalculator = yCoordinateCalculator;
_isDigitalLine = isDigitalLine;
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator" /> object that can be used to iterate through the collection.
/// </returns>
public virtual IEnumerator<Point> GetEnumerator()
{
return _isDigitalLine ?
(IEnumerator<Point>)new DigitalLinesIterator(_pointSeries, _xCoordinateCalculator, _yCoordinateCalculator) :
new LinesIterator(_pointSeries, _xCoordinateCalculator, _yCoordinateCalculator);
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator" /> object that can be used to iterate through the collection.
/// </returns>
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
However, when I try to do the following:
linesEnumerable = linesEnumerable.Concat(new[] { new Point(viewportWidth, lastYCoordinate) });
it says 'System.Collections.IEnumerable' does not contain a definition for 'Concat' and the best extension method overload 'System.Linq.Queryable.Concat(System.Linq.IQueryable, System.Collections.Generic.IEnumerable)' has some invalid arguments
I already have System.Linq namespace added
Anybody know why this is happening?

The compiler will give this error when the two collections are of different types T. For example:
List<int> l1 = new List<int>();
List<string> l2 = new List<string>();
var l3 = l1.Concat(l2);
var l4 = l1.Union(l2);
The Concat and Union calls will result in the following compile-time errors respectively:
'List' does not contain a definition for 'Concat' and the best extension method overload 'Queryable.Concat(IQueryable, IEnumerable)' requires a receiver of type 'IQueryable'
'List' does not contain a definition for 'Union' and the best extension method overload 'Queryable.Union(IQueryable, IEnumerable)' requires a receiver of type 'IQueryable'
It is confusing because the message is misleading and VS intellisense recognizes the extension methods. The solution is that l1 and l2 must be lists of the same type T.

Well this won't help you but this question is the top result when you google the error so I'm going to say what my problem was.
I had the following classes:
class Group
class Row : Group
class Column : Group
I was trying to call Concat on an IEnumerable<Row> with an IEnumerable<Column> to get an IEnumerable<Group>. This doesn't work because you can't convert the columns to rows. The solution was to cast my IEnumerable<Row> to IEnumerable<Group>.
e.g. rows.Cast<Group>().Concat(columns)

StyleCop SA1620, I don't know how to resolve my XML Comments to its liking

I have the following code w/comments: (It does compile)
/// <summary>
/// return a passing result of a particular type
/// </summary>
/// <typeparam name="T">Type of the value to be returned</typeparam>
/// <param name="value">the value to be returned</param>
/// <returns>a passing result</returns>
public static Result<T> Pass(T value)
{
return new Result<T>()
{
Passed = true,
Value = value
};
}
I get the following warning with it:
Warning 1 SA1620 : CSharp.Documentation :
The typeparam tags in the documentation header must
match the generic types for the method.
I did look at the help page for this error, which gives this explanation:
To fix a violation of this rule, add and fill-in one tag
for each generic type parameter on the element, and make sure that
the tags appear in the same order as the element’s type
parameters.
And it has provided sample code:
/// <summary>
/// A sample generic class.
/// </summary>
/// <typeparam name="S">The first generic type parameter.</typeparam>
/// <typeparam name="T">The second generic type parameter.</typeparam>
public class Class1<S, T>
{
}
I don't see anything about mine that breaks the standards it is showing, and I have tried various odd things, but I have no real idea of what I'm supposed to do here.

The only way that this can compile is if this method is inside a class that is generic in T. This method doesn't have any type parameters. If it was generic, there would be type parameters after the name of the method:
public static Result<T> Pass<T>(T value)
{
return new Result<T>()
{
Passed = true,
Value = value
};
}
But that's not the case with your method. So it must be:
class SomeClass<T>
{
public static Result<T> Pass(T value)
{
return new Result<T>()
{
Passed = true,
Value = value
};
}
}
And any documentation about the type parameter belongs up at the class level. E.g.:
/// <summary>
/// This is a result class
/// </summary>
/// <typeparam name="T">Type of the value to be returned</typeparam>
public class Result<T>
{
public bool Passed { get; set; }
public T Value { get; set; }
/// <summary>
/// return a passing result of a particular type
/// </summary>
/// <param name="value">the value to be returned</param>
/// <returns>a passing result</returns>
public static Result<T> Pass(T value)
{
return new Result<T>()
{
Passed = true,
Value = value
};
}
}

Moles and AppSettingsReader?

I'm working with Moles to write some unit tests. I searched online but I don't see any responses on how to use Moles to intercept the calls to AppSettingsReader.GetValue.
Has anyone been able to do this using Moles? Or am I forced into isolating the calls in my own class I can inject or mock? Ideally there is a way to directly use Moles to intercept the calls because we don't really want to modify the code we're looking to put under test.
Thanks!

Firstly, I strongly recommend moving to the release version of Moles, called "Fakes and Stubs", in .NET 4.5 / C# 5 / Visual Studio 2012.
The System.Configurations namespace is incompatible with the Mole/Fake type, and must be stubbed. To create a stub using the Moles Framework, simply create an interface for the System.Configuration.AppSettingsReader type. The Moles compiler will automatically convert the interface into a Stub type.
Here's an interface you can add to your project:
using System;
namespace YOUR_NAMESPACE_HERE
{
/// <summary>
/// IOC object for stubbing System.Configuration.AppSettingsReader.
/// Provides a method for reading values of a particular type from
/// the configuration.
/// </summary>
interface IAppSettingsReader
{
/// <summary>
/// Gets the value for a specified key from the
/// System.Configuration.ConfigurationSettings.AppSettings property
/// and returns an object of the specified type containing the
/// value from the configuration.
/// </summary>
/// <param name="key">The key for which to get the value.</param>
/// <param name="type">The type of the object to return.</param>
/// <returns>The value of the specified key</returns>
/// <exception cref="System.ArgumentNullException">key is null.
/// - or -
/// type is null.</exception>
/// <exception cref="System.InvalidOperationException">key does
/// not exist in the <appSettings> configuration section.
/// - or -
/// The value in the <appSettings> configuration section
/// for key is not of type type.</exception>
public object GetValue(string key, Type type);
}
}
Here's a stub class, too:
using System;
using System.Configuration;
namespace YOUR_NAMESPACE_HERE
{
/// <summary>
/// Production stub for System.Configuration.AppSettingsReader.
/// Provides a method for reading values of a particular type from
/// the configuration.
/// </summary>
public class AppSettingsReaderStub : IAppSettingsReader
{
/// <summary>
/// Gets the value for a specified key from the
/// System.Configuration.ConfigurationSettings.AppSettings property
/// and returns an object of the specified type containing the value
/// from the configuration.
/// </summary>
/// <param name="key">The key for which to get the value.</param>
/// <param name="type">The type of the object to return.</param>
/// <returns>The value of the specified key</returns>
/// <exception cref="System.ArgumentNullException">key is null.
/// - or -
/// type is null.</exception>
/// <exception cref="System.InvalidOperationException">key does not
/// exist in the <appSettings> configuration section.
/// - or -
/// The value in the <appSettings> configuration section for
/// key is not of type type.</exception>
public object GetValue(string key, Type type)
{
var reader = new AppSettingsReader();
object result = reader.GetValue(key, type);
return result;
}
}
}