I struggling to get something done when it suppose to be very easy to implement
say I have a car object
public class tblCarObj
{
public String Model;
public Int32 Year;
}
within these lines there is an implementation of reflection that is based on the fact that the object members are unknown (is this the only reason?)
which is nice for a generic functionality, but I am sacrificing functionality for performance if needed. and I wonder why both Links (see below) uses this approach.
can I simply use MyCarReader<tblCarObj>
instead of
//for this instance.
private IEnumerator<T> enumerator = null;
//List of all public fields in <T>
private List<FieldInfo> fields = new List<FieldInfo>();
public MyGenericDataReader(IEnumerable<T> enumerator)
{
this.enumerator = enumerator.GetEnumerator();
//Find the enumerator of all public fields
foreach (FieldInfo fieldinfo in typeof(T).GetFields(
BindingFlags.Instance |
BindingFlags.Public))
{
fields.Add(fieldinfo);
}
}
is there a way to implement this method without the use of reflection ?
background
the task Is to simply upload a collection of objects into database table,
List<tblCarObj>
where:
DataBase Table is Ready
DataBase Table matches the DataObject members
both are known at compile time.
and directly use it on SQLBulckCopy instead of a more complex object such as DataTable
MyGenericDataReader.cs
GenericListDataReader.cs
You are asking the runtime and the compiler to do something that it cannot do without reflecting over the type.
The information that allows the CLR and the compiler to know what properties are on the type are in the type's metadata. Reflection is the mechanism that queries metadata and serves it up in a meaningful way so that we can use it to discover the shape and content of a type. Without it, a type is essentially a named black box.
You could do what you want, but you'd have to code it by hand. The reason the libraries out there exist is because reflection makes it possible for you to avoid that extra work.
needs further test to try
eliminate unnecessary mappings Update: tested ok
(gain extra performance when MyTestObject properties/fields are same as columns)
if making it generic will effect it only slightly the use it with T
using :
public string sqlCon ="data source=(local);Initial Catalog=XXX;Integrated Security=True";
public SqlCommand Cmd;
public SqlConnection Conn;
public SqlDataReader Drdr;
public Form1()
{
InitializeComponent();
this.Conn = new SqlConnection(this.sqlCon);
this.Cmd = new SqlCommand("select * from [tblTestBC]", this.Conn);
useBulkCopy();
}
void justread()
{
this.Cmd.Connection.Open();
this.Drdr = this.Cmd.ExecuteReader();
if (this.Drdr.HasRows)
while (this.Drdr.Read())
{
}
this.Cmd.Connection.Close();
}
void useBulkCopy()
{
var bulkCopy = new SqlBulkCopy(this.Cmd.Connection);
bulkCopy.DestinationTableName = "tblTestBC";
//bulkCopy.ColumnMappings.Add("age", "age");
//bulkCopy.ColumnMappings.Add("name", "name");
this.Cmd.Connection.Open();
try
{
using (var dataReader = new mySimpleDataReader())
{
bulkCopy.WriteToServer(dataReader);
}
this.Cmd.Connection.Close();
}
catch (Exception e)
{
}
}
GenericIdataReader
namespace GenericIdataReader
{
public class MyTestObject
{
public int age;
public string name;
}
public class mySimpleDataReader : IDataReader
{
private IEnumerator<MyTestObject> enumerator = null;
public List<MyTestObject> prpLst { get; set; }
List<MyTestObject> lst()
{
var rt = new List<MyTestObject>(5);
for (int i = 0; i < rt.Capacity; i++)
{
var tmp = new MyTestObject { age = i, name = "MyTestObject->"+i };
rt.Add(tmp);
}
return rt;
}
public mySimpleDataReader()
{
this.prpLst = this.lst();
this.enumerator = this.prpLst.GetEnumerator();
}
public void Close()
{
throw new NotImplementedException();
}
public int Depth
{
get { throw new NotImplementedException(); }
}
public DataTable GetSchemaTable()
{
throw new NotImplementedException();
}
public bool IsClosed
{
get { throw new NotImplementedException(); }
}
public bool NextResult()
{
throw new NotImplementedException();
}
public bool Read()
{
return enumerator.MoveNext();
}
public int RecordsAffected
{
get { throw new NotImplementedException(); }
}
public void Dispose()
{
this.enumerator.Dispose();
}
public int FieldCount
{
get { return 2; }// must be setted
}
public bool GetBoolean(int i)
{
throw new NotImplementedException();
}
public byte GetByte(int i)
{
throw new NotImplementedException();
}
public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length)
{
throw new NotImplementedException();
}
public char GetChar(int i)
{
throw new NotImplementedException();
}
public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length)
{
throw new NotImplementedException();
}
public IDataReader GetData(int i)
{
throw new NotImplementedException();
}
public string GetDataTypeName(int i)
{
throw new NotImplementedException();
}
public DateTime GetDateTime(int i)
{
throw new NotImplementedException();
}
public decimal GetDecimal(int i)
{
throw new NotImplementedException();
}
public double GetDouble(int i)
{
throw new NotImplementedException();
}
public Type GetFieldType(int i)
{
throw new NotImplementedException();
}
public float GetFloat(int i)
{
throw new NotImplementedException();
}
public Guid GetGuid(int i)
{
throw new NotImplementedException();
}
public short GetInt16(int i)
{
throw new NotImplementedException();
}
public int GetInt32(int i)
{
throw new NotImplementedException();
}
public long GetInt64(int i)
{
throw new NotImplementedException();
}
public string GetName(int i)
{
throw new NotImplementedException();
}
public int GetOrdinal(string name)
{
throw new NotImplementedException();
}
public string GetString(int i)
{
throw new NotImplementedException();
}
public object GetValue(int i) // this is where data is being pooled
{
if (i > 0) return enumerator.Current.name;
// so need to create an object that will hold numeric index or simply change
//this to return an indexed object instead of an enumerator according to parmeter i value
return enumerator.Current.age;
}
public int GetValues(object[] values)
{
throw new NotImplementedException();
}
public bool IsDBNull(int i)
{
throw new NotImplementedException();
}
public object this[string name]
{
get { throw new NotImplementedException(); }
}
public object this[int i]
{
get { throw new NotImplementedException(); }
}
}
}
Related
I am writing unit tests with mongo db and I need to test somehow methods that works with data returned from mongo. For example method
IFindFluent<Transcript, Transcript> GetTranscriptByUserId(int userId);
Should return some transcript. But instead it returns interface that has couple of props - Filter, Options, Sort, and other.
I am going to test method Paginane of Paginator<T> class
public PaginatedObject<T> Paginate(IFindFluent<T,T> items, int limit, int page)
{
if (limit == 0)
{
limit = 10;
}
int count = (int)items.Count();
var lastPage = (count / limit) + 1;
if (page <= 0)
{
page = 1;
}
if (page > lastPage)
{
page = lastPage;
}
var request = items.Skip((page - 1) * limit).Limit(limit);
var itemsToReturn = request.ToList();
var pages = new PaginatedObject<T>
{
Entries = itemsToReturn,
Limit = limit,
Total = count,
Page = page
};
return pages;
}
First param is interface IFindFluent<T,T> items. So, I should mock it to return items when I call Count, Skip and Limit. But these methods could be easily mocked.
mockIfindFluent = new Mock<IFindFluent<Transcript, Transcript>>();
mockIfindFluent.Setup(s => s.Limit(It.IsAny<int>())).Returns(mockIfindFluent.Object);
mockIfindFluent.Setup(i => i.Skip(It.IsAny<int>())).Returns(mockIfindFluent.Object);
mockIfindFluent.Setup(i => i.Count(CancellationToken.None)).Returns(3);
Real problem I have when I call ToList().
I got exception that I can not mock property that does not belong to model and so on.
Took some inspiration from this https://gist.github.com/mizrael/a061331ff5849bf03bf2 and extended implementation which worked for me. I have created a fake implementation of the IFindFluent interface and it had a dependency on the IAsyncCursor interface, so I did a fake implementation of that also and using that in return of mock method I wanted to set up. In that fake implementation, I have initialized an enumerable and returned that in a method I am using. You can still be more creative and play around whatever you want to return. So far this worked for me.
Here is a fake implementation.
public class FakeFindFluent<TEntity, TProjection> : IFindFluent<TEntity, TEntity>
{
private readonly IEnumerable<TEntity> _items;
public FakeFindFluent(IEnumerable<TEntity> items)
{
_items = items ?? Enumerable.Empty<TEntity>();
}
public FilterDefinition<TEntity> Filter { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
public FindOptions<TEntity, TEntity> Options => throw new NotImplementedException();
public IFindFluent<TEntity, TResult> As<TResult>(MongoDB.Bson.Serialization.IBsonSerializer<TResult> resultSerializer = null)
{
throw new NotImplementedException();
}
public long Count(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public Task<long> CountAsync(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public long CountDocuments(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public Task<long> CountDocumentsAsync(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public IFindFluent<TEntity, TEntity> Limit(int? limit)
{
throw new NotImplementedException();
}
public IFindFluent<TEntity, TNewProjection> Project<TNewProjection>(ProjectionDefinition<TEntity, TNewProjection> projection)
{
throw new NotImplementedException();
}
public IFindFluent<TEntity, TEntity> Skip(int? skip)
{
throw new NotImplementedException();
}
public IFindFluent<TEntity, TEntity> Sort(SortDefinition<TEntity> sort)
{
throw new NotImplementedException();
}
public IAsyncCursor<TEntity> ToCursor(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public Task<IAsyncCursor<TEntity>> ToCursorAsync(CancellationToken cancellationToken = default)
{
IAsyncCursor<TEntity> cursor = new FakeAsyncCursor<TEntity>(_items);
var task = Task.FromResult(cursor);
return task;
}
}
public class FakeAsyncCursor<TEntity> : IAsyncCursor<TEntity>
{
private IEnumerable<TEntity> items;
public FakeAsyncCursor(IEnumerable<TEntity> items)
{
this.items = items;
}
public IEnumerable<TEntity> Current => items;
public void Dispose()
{
//throw new NotImplementedException();
}
public bool MoveNext(CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
public Task<bool> MoveNextAsync(CancellationToken cancellationToken = default)
{
return Task.FromResult(false);
}
}
Here is how I set up my mock method to return what I wanted for my unit testing.
mockParticipantRepository
.Setup(x => x.FindByFilter(It.IsAny<FilterDefinition<Participant>>()))
.Returns(new FakeFindFluent<Participant, Participant>(participantsByRelation));
I hope this is helpful.
I have an interface that is implemented by all of my classes which are responsible for exporting data to different formats.
Sample code:
public interface IExport
{
string Exporter();
}
public class ExcelExport : IExport
{
public string Exporter()
{
return "excel";
}
}
public class PdfExport : IExport
{
public string Exporter()
{
return "pdf";
}
}
I want to get a specific type in runtime, so I know I have to use abstract factory, but don't I know how tp in this example.
Exports are handled by the manager class:
public interface IExportManager
{
IExport GetExportProvider(ExportType type);
}
public interface IExportFactory
{
IExport CreateExport(ExportType type);
}
public class ExportManager : IExportManager
{
private IExportFactory exportFactory;
public ExportManager(IExportFactory exportFactory)
{
this.exportFactory = exportFactory;
}
public IExport GetExportProvider(ExportType type)
{
return exportFactory.CreateExport(type);
}
}
public enum ExportType
{
PDF,
XLSX
}
How can I get the right object instance depending on the type parameter using the GetExportProvider methods?
This is my Ninject module:
public class NinModule : NinjectModule
{
public override void Load()
{
this.Bind<IExportFactory>().ToFactory();
this.Bind<IExportManager>().To<ExportManager>();
this.Bind<IExport>().To<ExcelExport>();//.WhenInjectedInto<IExportManager>().WithPropertyValue("type", ExportType.XLSX);
this.Bind<IExport>().To<PdfExport>();//.WhenInjectedInto<IExportManager>().WithPropertyValue("type", ExportType.PDF);
}
}
And the code used to test it:
static void Main(string[] args)
{
IKernel k = new StandardKernel(new NinModule());
IExportManager r = k.Get<IExportManager>();
var pdf = r.GetExportProvider(ExportType.PDF);
Console.WriteLine(pdf.Exporter());
Console.Read();
}
Thanks in advance for your help.
I don't know anything about Ninject, but strictly from a C# perspective, why wouldn't this work...
public class ExportFactory : IExportFactory
{
public IExport CreateExport(ExportType type)
{
switch(type)
{
case ExportType.PDF:
return new PdfExport();
case ExportType.XLSX
return new ExcelExport();
}
}
}
I think you need to create dynamic binding in ExportFactory class.
Something like this:
if (exportType == ExportType.PDF)
{
Bind<IExport>().To<PdfExport>().InRequestScope();
}
else if (exportType == ExportType.XLSX)
{
Bind<IExport>().To<ExcelExport>().InRequestScope();
}
Alright, finally I got the solution.
One possibility is to create a custom provider:
public class ExportProvider : Provider<IExport>
{
protected override IExport CreateInstance(IContext context)
{
ExportType type = (ExportType)context.Parameters.First().GetValue(context, null);
switch (type)
{
case ExportType.PDF: return new PdfExport();
case ExportType.XLSX: return new ExcelExport();
}
return null;
}
}
And config: this.Bind<IExport>().ToProvider<ExportProvider>();
Second possibility I have found:
this.Bind<IExport>().To<ExcelExport>().When((q) =>
{
ExportType type = (ExportType)q.Parameters.First().GetValue(new DummyContext(), null);
return type == ExportType.XLSX;
});
this.Bind<IExport>().To<PdfExport>().When((q) =>
{
ExportType type = (ExportType)q.Parameters.First().GetValue(new DummyContext(), null);
return type == ExportType.PDF;
});
The GetValue of IParameter requires not null IContext provided. In the When clause we can't get any, but we can use diffrent one, because this parameter is not checked in the method as it look like. So we can create a simple class that implements the IContext interface:
public class DummyContext : IContext
{
public Ninject.Planning.Bindings.IBinding Binding
{
get { throw new NotImplementedException(); }
}
public Type[] GenericArguments
{
get { throw new NotImplementedException(); }
}
public IProvider GetProvider()
{
throw new NotImplementedException();
}
public object GetScope()
{
throw new NotImplementedException();
}
public bool HasInferredGenericArguments
{
get { throw new NotImplementedException(); }
}
public IKernel Kernel
{
get { throw new NotImplementedException(); }
}
public ICollection<IParameter> Parameters
{
get { throw new NotImplementedException(); }
}
public Ninject.Planning.IPlan Plan
{
get
{
throw new NotImplementedException();
}
set
{
throw new NotImplementedException();
}
}
public IRequest Request
{
get { throw new NotImplementedException(); }
}
public object Resolve()
{
throw new NotImplementedException();
}
}
I am pretty new to Generic class in C#. I was trying to create one and ran into compiler error that I am not sure how to get around it.
Basically, I have a class G that implements ICollection
public class G<T> : ICollection<T> where T : IEqualityComparer
{
private ArrayList _members = new ArrayList();
public void Add(T item)
{
throw new NotImplementedException();
}
public void Clear()
{
throw new NotImplementedException();
}
public bool Contains(T item)
{
throw new NotImplementedException();
}
public void CopyTo(T[] array, int arrayIndex)
{
throw new NotImplementedException();
}
public int Count
{
get { throw new NotImplementedException(); }
}
public bool IsReadOnly
{
get { throw new NotImplementedException(); }
}
public bool Remove(T item)
{
throw new NotImplementedException();
}
public IEnumerator<T> GetEnumerator()
{
foreach (var item in _members)
{
yield return (T)item;
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}
I wanted to be able to do comparison in G and Find item in G, so I have put a constraint that T has to be implementing IEqualityComparer. Then, I have an actual class called IntegerClass that implement IEqualityComparer as below. So far, so good, no compiler error.
public class IntegerClass : IEqualityComparer<int>
{
public bool Equals(int x, int y)
{
throw new NotImplementedException();
}
public int GetHashCode(int obj)
{
throw new NotImplementedException();
}
}
However, when I tried to create an instance of G above. I got a compiler error.
class Program
{
static void Main(string[] args)
{
G<IntegerClass> i = new G<IntegerClass>();
}
}
The error is:
The type 'TestGeneric.IntegerClass' cannot be used as type parameter 'T' in the generic type or method 'TestGeneric.G<T>'.
There is no implicit reference conversion from 'TestGeneric.IntegerClass' to 'System.Collections.IEqualityComparer'
Could someone pinpoint what I have overlooked? Why would I need conversion? All I did was replacing class T with IntegerClass that implements IEqualityComparer interface. What should I do otherwise? I am new to this generic stuff, but have found it quite useful. I am thinking it could be very useful if I understand it correctly. Please help.
Update:
Based on some suggestion, I saw what was wrong and I updated the code as follow:
public class IntegerClass : IEqualityComparer
{
public bool Equals(object x, object y)
{
throw new NotImplementedException();
}
public int GetHashCode(object obj)
{
throw new NotImplementedException();
}
}
public class G<T> : ICollection<T> where T : IEqualityComparer
{
private ArrayList _members = new ArrayList();
public void Add(T item)
{
throw new NotImplementedException();
}
public void Clear()
{
throw new NotImplementedException();
}
public bool Contains(T item)
{
throw new NotImplementedException();
}
public void CopyTo(T[] array, int arrayIndex)
{
throw new NotImplementedException();
}
public int Count
{
get { throw new NotImplementedException(); }
}
public bool IsReadOnly
{
get { throw new NotImplementedException(); }
}
public bool Remove(T item)
{
throw new NotImplementedException();
}
public IEnumerator<T> GetEnumerator()
{
foreach (var item in _members)
{
yield return (T)item;
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}
I think it might work but I got the warning below:
'TestGeneric.IntegerClass.Equals(object, object)' hides inherited member 'object.Equals(object, object)'. Use the new keyword if hiding was intended.
I know object has an Equals methods but the warning does not make sense. Should it say use the new keyword if hiding was NOT intended?
Your constraint refers to the non-generic System.Collections.IEqualityComparer interface, which is not the same as IEqualityComparer<T>.
You could fix that error by specify the generic type in the constraint.
However, that's not what you want; an IEqualityComparer is a class that compares other things.
You want where T : IEquatable<T>.
change your IntegerClass like below.
public class IntegerClass : IEqualityComparer<IntegerClass>
{
public bool Equals(IntegerClass IC1, IntegerClass IC2)
{
throw new NotImplementedException();
}
public int GetHashCode(IntegerClass obj)
{
throw new NotImplementedException();
}
}
Or you could resort it to the fact that Objects has an equality function.
Hence, this would work
public interface IMyComparer
{
object Comparer { get; }
}
public class IntegerClass : IMyComparer, IEqualityComparer<int>
{
public object Comparer { get { return this; } }
public bool Equals(int x, int y)
{
throw new NotImplementedException();
}
public int GetHashCode(int obj)
{
throw new NotImplementedException();
}
}
public class G<T> : ICollection<T> where T : IMyComparer
{
Your implementations
}
Hope it helps.
I have been working with a project for last 4 months. We are using a custom framework for the development. The problem I am talking about, was working for all other classes. But for the first time I am facing this weird incident. Now Straight to break point.
My framework code is like
public static List<ViewNotSetBillableCoursesEntity> GetAllNotSetBillableCources()
{
try
{
List<ViewNotSetBillableCoursesEntity> entities = new List<ViewNotSetBillableCoursesEntity>();
string command = SELECT;
SqlConnection sqlConnection = MSSqlConnectionHandler.GetConnection();
SqlDataReader dataReader = QueryHandler.ExecuteSelect(command, sqlConnection);
entities = Maps(dataReader);
dataReader.Close();
return entities;
}
catch (Exception exception)
{
throw exception;
}
}
In the above method the dataReader is sent to Maps method.
The Maps method is ......
private static List<ViewNotSetBillableCoursesEntity> Maps(SqlDataReader theReader)
{
SQLNullHandler nullHandler = new SQLNullHandler(theReader);
// the incident is happening here, the SQLNullHandler is given below.
List<ViewNotSetBillableCoursesEntity> entities = null;
while (theReader.Read())
{
if (entities == null)
{
entities = new List<ViewNotSetBillableCoursesEntity>();
}
ViewNotSetBillableCoursesEntity entity = Mapper(nullHandler);
entities.Add(entity);
}
return entities;
}
The SQLNullHandler is given below:
puplic Class SQLNullHandler
{
private IDataReader _reader;
public SQLNullHandler(IDataReader reader)
{
_reader = reader;
}
#region Get Null value
public static object GetNullValue(int Value)
{
if(Value==0)
{
return null;
}
else
{
return Value;
}
}
public static object GetNullValue(double Value)
{
if (Value == 0)
{
return null;
}
else
{
return Value;
}
}
public static object GetNullValue(decimal Value)
{
if (Value == 0)
{
return null;
}
else
{
return Value;
}
}
public static object GetNullValue(DateTime Value)
{
if(DateTime.MinValue==Value)
{
return null;
}
else
{
return Value;
}
}
public static object GetNullValue(string Value)
{
if(Value.Length<=0)
{
return null;
}
else
{
return Value;
}
}
#endregion
public IDataReader Reader
{
get{return _reader;}
}
public bool IsNull(int index)
{
return _reader.IsDBNull(index);
}
public int GetInt32(int i)
{
return _reader.IsDBNull(i)? 0 : _reader.GetInt32(i);
}
public byte GetByte(int i)
{
return _reader.IsDBNull(i)? (byte)0 : _reader.GetByte(i);
}
//and so on for all possible type for this app
}
The Funny thing is for all these classes these methods and lines of code work very fine, but in this scenario after the line SQLNullHandler nullHandler = new SQLNullHandler(theReader); the datareder becomes empty.
My questions are
Why is this Happening and next,
what can be done to solve this problem?
Given this magical interface:
public interface IHat<out TRabbit>
{
TRabbit Take();
}
And this class hierarchy:
public class Rabbit { }
public class WhiteRabbit : Rabbit { }
I can now compile this:
IHat<WhiteRabbit> hat1 = null;
IHat<Rabbit> hat2 = hat1;
Which is great. But what if I define the interface differently:
public interface IHat<out TRabbit>
{
bool Take(out TRabbit r);
}
I'm indicating that the hat might be empty, using a separate boolean return value (the previous version would perhaps have returned a null rabbit from an empty hat). But I'm still only outputting a rabbit, so not doing anything logically different to the previous version.
The C# 4.0 compiler in the CTP gives an error in the interface definition - it requires 'out' method parameters to be of an invariant type. Is there a hard-and-fast reason why this isn't allowed, or is it something that might be addressed in a future version?
Interesting. However, at the CLI level there is no such thing as "out" - only "ref"; there is an attribute that helps compilers (for definite assignment) that says "you don't need to pass it in".
Maybe this restriction is because the CLI doesn't have "out", only "ref".
Although it's a bit of a hassle, you can use a covariance wrapper:
public class CovariantListWrapper<TOut, TIn> : IList<TOut> where TIn : TOut
{
IList<TIn> list;
public CovariantListWrapper(IList<TIn> list)
{
this.list = list;
}
public int IndexOf(TOut item)
{
// (not covariant but permitted)
return item is TIn ? list.IndexOf((TIn)item) : -1;
}
public TOut this[int index]
{
get { return list[index]; }
set { throw new InvalidOperationException(); }
}
public bool Contains(TOut item)
{
// (not covariant but permitted)
return item is TIn && list.Contains((TIn)item);
}
public void CopyTo(TOut[] array, int arrayIndex)
{
foreach (TOut t in this)
array[arrayIndex++] = t;
}
public int Count { get { return list.Count; } }
public bool IsReadOnly { get { return true; } }
public IEnumerator<TOut> GetEnumerator()
{
foreach (TIn t in list)
yield return t;
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public void Insert(int index, TOut item) { throw new InvalidOperationException(); }
public void RemoveAt(int index) { throw new InvalidOperationException(); }
public void Add(TOut item) { throw new InvalidOperationException(); }
public void Clear() { throw new InvalidOperationException(); }
public bool Remove(TOut item) { throw new InvalidOperationException(); }
}
This lets you keep the collection as it was originally typed and refer to it covariantly without creating a detached copy, so that updates to the original are seen in the covariant use. Example:
class CovarianceWrapperExample
{
class Person { }
class Employee : Person { }
void ProcessPeople(IList<Person> people) { /* ... */ }
void Foo()
{
List<Employee> employees = new List<Employee>();
// cannot do:
ProcessPeople(employees);
// can do:
ProcessPeople(new CovariantListWrapper<Person, Employee>(employees));
}
}