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Enums casting to a byte

Am using EntityFramework and have a LinkStatusID column which is a tinyint, which gets generated into a byte in C#.
public enum LinkStatus
{
Added = 0,
Deleted = 1
}
however this gives:
a.LinkStatusID = (byte)Enums.LinkStatus.Deleted;
is there a more elegant way to structure this?
EDIT2 for LastCoder:
public enum LinkStatus : byte
{
Added = 0,
Deleted = 1
}
var blah = Enums.LinkStatus.Added;
var ty = blah.GetType();
var blah2 = (byte)Enums.LinkStatus.Added;
var ty2 = blah2.GetType();
This doesn't work (as I expected) however the first answer here explains why.
EDIT3:
EF isn't the only way this sln gets to the DB, so I'm keen to keep the Enums explicit in the code. Thanks for EF5 Enum suggestions!

public enum LinkStatus : byte
Will avoid the explicit cast.

You should probably use the native enum support, like SLaks mentioned above (Tutorial is here). If you don't want to do that, you can do something else that I found for before EF supported it:
public int CountryInt{get;set;}
public Countries Country
{
get { return (Countries) this.CountryInt; }
set { this.CountryInt = (int) value; }
}
Using this, then, allows you to just set the Country variable, and have it automatically go to the DB as the correct int value.

A static class can be used as a workaround
public static class LinkStatus
{
public static byte
Added = 0,
Deleted = 1;
}

How to specify defaults for a plugin function in C#

I'm trying to implement a simple plugin system which will allow people to write the following:
[Plugin("A plugin function")]
public static int PluginFunction(int a, int b)
{
return a + b;
}
and then drop the DLL containing this function into a folder where it will be scanned by the application and show up as an available function at runtime. This all works fine, so far so good, the PluginAttribute class is what you would expect, just a description string for the function.
However, I'd like to allow the plugin writer to specify default values for the parameters. This is OK for values which are constant at compile time and then deduced via reflection, but I'd like a way to specify defaults for more complex types which will be created at runtime. Has anyone implemented something similar? The primary goal is to make it simple to implement plugin functions - I'm trying to avoid complex scaffolding but accept that my nice simple system is not going to cut it if I want this feature. I'm also happy to have some complexity in the application code which makes the system appear simple to the plugin writer.
Thanks,
Charlie.
Update:
I'm going with a combination of what's been suggested here, the closest is what Peter O. came up with - here's a version:
[Plugin("A plugin function")]
[Defaults(typeof(AdderDefaults))]
public static int Adder(int a, int b)
{
return a + b;
}
public static class AdderDefaults
{
public static int a { get { return 1; } }
public static int b { get { return 2; } }
}
[Plugin("Another plugin function")]
[Defaults(typeof(TexturizerDefaults))]
public static Bitmap Texturize(Bitmap source, Point offset)
{
return result;
}
public static class TexturizerDefaults
{
// no default for source parameter
public static Point offset { get { return new Point(16, 16); } }
}
This allows parameters to be skipped and specified by name. No compile time checking but that's OK - checking these at runtime is acceptable.

Maybe you can create an attribute which refers to a type
containing default values for the plugin. Example:
[PluginDefaults(typeof(MyPluginDefaults))]
The class MyPluginDefaults could then look like:
public class MyPluginDefaults {
int Parameter1 { // First parameter
get { return 0; } // default value for 'a'
}
int Parameter2 { // Second parameter
get { return 4; } // default value for 'b'
}
// Additional parameters would be called Parameter3, Parameter4, and so on.
}

There are lots of way to do that, the simpliest is to use a simple convention :
[Plugin("A plugin function")]
public static int PluginFunction(int a, int b)
{
return a + b;
}
public static object[] PluginFunctionDefaultArguments()
{
return new [] { 0, 0 };
}
Each time you find a function marked with PluginAttribute search for a function having the same name with the DefaultArguments sufix, no parameters and an object[] return type. Then call it and store the values somewhere. You should also support the default values to be specifed using the dedicated C#/VB syntax (it is found in the DefaultValue member for the parameter)

One way would be to have property Defaults for each of the classes. It returns an object that can be queried for the defaults, for example like this:
object[] pluginFunctionDefaults = FooPlugin.Defaults["PluginFunction"];
(Obviously, you wouldn't have code exactly like this in your application.)
And the declaration of the defaults could look like this:
class FooPlugin
{
static FooPlugin()
{
var bar = new Bar();
Defaults = new DefaultValues()
.Add(() => PluginFunction(42, 13))
.Add(() => AnotherFunction(bar));
}
public static DefaultValues Defaults { get; private set; }
// actual methods of the class
}
Using expressions like this means that the types of the defaults are checked at compile time. The DefaultValues class parses the expressions and stores the parameters. It could look something like this:
class DefaultValues
{
private readonly Dictionary<string, object[]> m_expressions =
new Dictionary<string, object[]>();
public DefaultValues Add<T>(Expression<Func<T>> func)
{
var methodCall = ((MethodCallExpression)func.Body);
var name = methodCall.Method.Name;
var arguments =
methodCall.Arguments
.Select(Evaluate)
.ToArray();
m_expressions.Add(name, arguments);
return this;
}
private static object Evaluate(Expression expression)
{
return Expression.Lambda<Func<object>>(
Expression.Convert(expression, typeof(object)))
.Compile()();
}
public object[] this[string methodName]
{
get { return m_expressions[methodName]; }
}
}

Using LINQ to create a List<T> where T : someClass<U>

This is related to a prior question of mine C# Generic List conversion to Class implementing List<T>
I have the following code:
public abstract class DataField
{
public string Name { get; set; }
}
public class DataField<T> : DataField
{
public T Value { get; set; }
}
public static List<DataField> ConvertXML(XMLDocument data) {
result = (from d in XDocument.Parse(data.OuterXML).Root.Decendendants()
select new DataField<string>
{
Name = d.Name.ToString(),
Value = d.Value
}).Cast<DataField>().ToList();
return result;
}
This works however I would like to be able to modify the select portion of the LINQ query to be something like this:
select new DataField<[type defined in attribute of XML Element]>
{
Name = d.Name.ToString(),
Value = d.Value
}
Is this just a poor approach? is it possible? Any suggestions?

Here is a working solution: (You must specify fully qualified type names for your Type attribute otherwise you have to configure a mapping somehow...)
I used the dynamic keyword, you can use reflection to set the value instead if you do not have C# 4...
public static void Test()
{
string xmlData = "<root><Name1 Type=\"System.String\">Value1</Name1><Name2 Type=\"System.Int32\">324</Name2></root>";
List<DataField> dataFieldList = DataField.ConvertXML(xmlData);
Debug.Assert(dataFieldList.Count == 2);
Debug.Assert(dataFieldList[0].GetType() == typeof(DataField<string>));
Debug.Assert(dataFieldList[1].GetType() == typeof(DataField<int>));
}
public abstract class DataField
{
public string Name { get; set; }
/// <summary>
/// Instanciate a generic DataField<T> given an XElement
/// </summary>
public static DataField CreateDataField(XElement element)
{
//Determine the type of element we deal with
string elementTypeName = element.Attribute("Type").Value;
Type elementType = Type.GetType(elementTypeName);
//Instanciate a new Generic element of type: DataField<T>
dynamic dataField = Activator.CreateInstance(typeof(DataField<>).MakeGenericType(elementType));
dataField.Name = element.Name.ToString();
//Convert the inner value to the target element type
dynamic value = Convert.ChangeType(element.Value, elementType);
//Set the value into DataField
dataField.Value = value;
return dataField;
}
/// <summary>
/// Take all the descendant of the root node and creates a DataField for each
/// </summary>
public static List<DataField> ConvertXML(string xmlData)
{
var result = (from d in XDocument.Parse(xmlData).Root.DescendantNodes().OfType<XElement>()
select CreateDataField(d)).ToList();
return result;
}
}
public class DataField<T> : DataField
{
public T Value { get; set; }
}

You cannot do this easily in C#. The generic type argument has to specified at compile time. You can use reflection to do otherwise
int X = 1;
Type listype = typeof(List<>);
Type constructed = listype.MakeGenericType( X.GetType() );
object runtimeList = Activator.CreateInstance(constructed);
Here we have just created a List<int>. You can do it with your type

Different instances of a generic class are actually different classes.
I.e. DataField<string> and DataField<int> are not the same class at all(!)
This means, that you can not define the generic parameter during run-time, as it has to be determined during compile-time.

I would say this is a poor approach. In reality, even after you parse your XML file, you're not going to know what types of "DataFields" you have. You might as well just parse them as objects.
However, if you know that you're only ever going to have x number of types, you can do like so:
var Dictionary<string, Func<string, string, DataField>> myFactoryMaps =
{
{"Type1", (name, value) => { return new DataField<Type1>(name, Type1.Parse(value); } },
{"Type2", (name, value) => { return new DataField<Type2>(name, Type2.Parse(value); } },
};

Termit's answer is certainly excellent. Here is a little variant.
public abstract class DataField
{
public string Name { get; set; }
}
public class DataField<T> : DataField
{
public T Value { get; set; }
public Type GenericType { get { return this.Value.GetType(); } }
}
static Func<XElement , DataField> dfSelector = new Func<XElement , DataField>( e =>
{
string strType = e.Attribute( "type" ).Value;
//if you dont have an attribute type, you could call an extension method to figure out the type (with regex patterns)
//that would only work for struct
Type type = Type.GetType( strType );
dynamic df = Activator.CreateInstance( typeof( DataField<>).MakeGenericType( type ) );
df.Name = e.Attribute( "name" ).Value;
dynamic value = Convert.ChangeType( e.Value , type );
df.Value = value;
return df;
} );
public static List<DataField> ConvertXML( string xmlstring )
{
var result = XDocument.Parse( xmlstring )
.Root.Descendants("object")
.Select( dfSelector )
.ToList();
return result;
}
static void Main( string[] args )
{
string xml = "<root><object name=\"im1\" type=\"System.String\">HelloWorld!</object><object name=\"im2\" type=\"System.Int32\">324</object></root>";
List<DataField> dfs = ConvertXML( xml );
}

you can create generic type by reflection
var instance = Activator.CreateInstance( typeof(DataField)
.MakeGenericType(Type.GetType(typeNameFromAttribute) );
// and here set properties also by reflection

#Termit and #Burnzy put forward good solutions involving factory methods.
The problem with that is that you're loading up your parsing routine with a bunch of extra logic (more testing, more errors) for dubious returns.
Another way to do it would be to use a simplified string-based DataField with typed read methods - the top answer for this question.
An implementation of a typed-value method that would be nice but only works for value types (which does not include strings but does include DateTimes):
public T? TypedValue<T>()
where T : struct
{
try { return (T?) Convert.ChangeType(this.Value, typeof(T)); }
catch { return null; }
}
I'm assuming that you're wanting to use the type information to do things like dynamically assigning user-controls to the field, validation rules, correct SQL types for persistence etc.
I've done a lot of this sort of thing with approaches that seem a bit like yours.
At the end of the day you should seperate your metadata from your code - #Burnzy's answer chooses the code based on the metadata (a "type" attribute of the DataField element) and is a very simple example of this.
If you're dealing with XML, XSDs are a very useful and extensible form of metadata.
As far as what you store each field's data in - use strings because:
they are nullable
they can store partial values
they can store invalid values (makes telling the user to sort their act out more transparent)
they can store lists
special cases won't invade unrelated code because there aren't any
learn regular expressions, validate, be happy
you can convert them to stronger types really easily
I found it very rewarding to develop little frameworks like this - it is a learning experience and you'll come out understanding a lot more about UX and the reality of modelling from it.
There are four groups of test cases that I would advise you to tackle first:
Dates, Times, Timestamps (what I call DateTime), Periods (Timespan)
in particular, make sure you test having a different server locality from the client's.
lists - multi-select foreign keys etc
null values
invalid input - this generally involves retaining the original value
Using strings simplifies all this greatly because it allows you to clearly demarcate responsibilities within your framework. Think about doing fields containing lists in your generic model - it gets hairy rather quickly and it is easy to end up with a special case for lists in pretty much every method. With strings, the buck stops there.
Finally, if you want a solid implementation of this sort of stuff without having to do anything much, consider DataSets - old school I know - they do all sorts of wonderful things you wouldn't expect but you do have to RTFM.
The main downfall of that idea would be that it isn't compatible with WPF data binding - though my experience has been that reality isn't compatible with WPF data binding.
I hope I interpreted your intentions correctly - good luck either way :)

Unfortunately, there no inheritance relation between C<T> and C<string> for instance.
However, you can inherit from a common non-generic class and in addition to this implement a generic interface.
Here I use explicit interface implementation in order to be able to declare a Value property typed as object, as well as a more specifically typed Value property.
The Values are read-only and can only be assigned through a typed constructor parameter. My construction is not perfect, but type safe and doesn't use reflection.
public interface IValue<T>
{
T Value { get; }
}
public abstract class DataField
{
public DataField(string name, object value)
{
Name = name;
Value = value;
}
public string Name { get; private set; }
public object Value { get; private set; }
}
public class StringDataField : DataField, IValue<string>
{
public StringDataField(string name, string value)
: base(name, value)
{
}
string IValue<string>.Value
{
get { return (string)Value; }
}
}
public class IntDataField : DataField, IValue<int>
{
public IntDataField(string name, int value)
: base(name, value)
{
}
int IValue<int>.Value
{
get { return (int)Value; }
}
}
The list can then be declared with the abstract base class DataField as generic parameter:
var list = new List<DataField>();
switch (fieldType) {
case "string":
list.Add(new StringDataField("Item", "Apple"));
break;
case "int":
list.Add(new IntDataField("Count", 12));
break;
}
Access the strongly typed field through the interface:
public void ProcessDataField(DataField field)
{
var stringField = field as IValue<string>;
if (stringField != null) {
string s = stringField.Value;
}
}

While the other questions mostly proposed an elegant solution to convert your XML elements to a generic class instance, I'm going to deal with the consequences of taking the approach to model the DataField class as a generic like DataField<[type defined in attribute of XML Element]>.
After selecting your DataField instance into the list you want to use these fields. Her polymorphism comes into play! You want to iterate your DataFields an treat them in a uniform way. Solutions that use generics often end up in a weird switch/if orgy since there is no easy way to associate behavior based on the generic type in c#.
You might have seen code like this (I'm trying to calculate the sum of all numeric DataField instances)
var list = new List<DataField>()
{
new DataField<int>() {Name = "int", Value = 2},
new DataField<string>() {Name = "string", Value = "stringValue"},
new DataField<float>() {Name = "string", Value = 2f},
};
var sum = 0.0;
foreach (var dataField in list)
{
if (dataField.GetType().IsGenericType)
{
if (dataField.GetType().GetGenericArguments()[0] == typeof(int))
{
sum += ((DataField<int>) dataField).Value;
}
else if (dataField.GetType().GetGenericArguments()[0] == typeof(float))
{
sum += ((DataField<float>)dataField).Value;
}
// ..
}
}
This code is a complete mess!
Let's go try the polymorphic implementation with your generic type DataField and add some method Sum to it that accepts the old some and returns the (possibly modified) new sum:
public class DataField<T> : DataField
{
public T Value { get; set; }
public override double Sum(double sum)
{
if (typeof(T) == typeof(int))
{
return sum + (int)Value; // Cannot really cast here!
}
else if (typeof(T) == typeof(float))
{
return sum + (float)Value; // Cannot really cast here!
}
// ...
return sum;
}
}
You can imagine that your iteration code gets a lot clearer now but you still have this weird switch/if statement in you code. And here comes the point: Generics do not help you here it's the wrong tool at the wrong place. Generics are designed in C# for giving you compile time type safety to avoid potential unsafe cast operations. They additionally add to code readability but that's not the case here :)
Let's take a look at the polymorphic solution:
public abstract class DataField
{
public string Name { get; set; }
public object Value { get; set; }
public abstract double Sum(double sum);
}
public class IntDataField : DataField
{
public override double Sum(double sum)
{
return (int)Value + sum;
}
}
public class FloatDataField : DataField
{
public override double Sum(double sum)
{
return (float)Value + sum;
}
}
I guess you will not need too much fantasy to imagine how much adds to your code's readability/quality.
The last point is how to create instances of these classes. Simply by using some convention TypeName + "DataField" and Activator:
Activator.CreateInstance("assemblyName", typeName);
Short Version:
Generics is not the appropriate approach for your problem because it does not add value to the handling of DataField instances. With the polymorphic approach you can work easily with the instances of DataField!

It's not impossible as you can do this with reflection. But this isn't what generics were designed for and isn't how it should be done. If you're going to use reflection to make the generic type, you may as well not use a generic type at all and just use the following class:
public class DataField
{
public string Name { get; set; }
public object Value { get; set; }
}

You'll need to insert the logic for determining the data type from your XML and add all the types you need to use but this should work:
result = (from d in XDocument.Parse(data.OuterXML).Root.Descendants()
let isString = true //Replace true with your logic to determine if it is a string.
let isInt = false //Replace false with your logic to determine if it is an integer.
let stringValue = isString ? (DataField)new DataField<string>
{
Name = d.Name.ToString(),
Value = d.Value
} : null
let intValue = isInt ? (DataField)new DataField<int>
{
Name = d.Name.ToString(),
Value = Int32.Parse(d.Value)
} : null
select stringValue ?? intValue).ToList();

C# "Enum" Serialization - Deserialization to Static Instance

Suppose you have the following class:
class Test : ISerializable {
public static Test Instance1 = new Test {
Value1 = "Hello"
,Value2 = 86
};
public static Test Instance2 = new Test {
Value1 = "World"
,Value2 = 26
};
public String Value1 { get; private set; }
public int Value2 { get; private set; }
public void GetObjectData(SerializationInfo info, StreamingContext context) {
//Serialize an indicator of which instance we are - Currently
//I am using the FieldInfo for the static reference.
}
}
I was wondering if it is possible / elegant to deserialize to the static instances of the class?
Since the deserialization routines (I'm using BinaryFormatter, though I'd imagine others would be similar) look for a constructor with the same argument list as GetObjectData(), it seems like this can't be done directly . . Which I would presume means that the most elegant solution would be to actually use an enum, and then provide some sort of translation mechanism for turning an enum value into an instance reference. However, I personally like that the "Enum"'s choices are directly linked with their data.
How might one go about this?

If you need more data with with the Enums, consider using attributes. Example below.
class Name : Attribute
{
public string Text;
public Name(string text)
{
this.Text = text;
}
}
class Description : Attribute
{
public string Text;
public Description(string text)
{
this.Text = text;
}
}
public enum DaysOfWeek
{
[Name("FirstDayOfWeek")]
[Description("This is the first day of 7 days")]
Sunday = 1,
[Name("SecondDayOfWeek")]
[Description("This is the second day of 7 days")]
Monday= 2,
[Name("FirstDayOfWeek")]
[Description("This is the Third day of 7 days")]
Tuesday= 3,
}
Perhaps this will allow you to provide more information with the Enums. You can access the attributes through reflection. If you need an example to retrieve the attribute I can provide that as well but I'm trying to keep this somewhat short.

Use Enum.Parse...Suppose you have the following:
Enum myEnum{
Foo = 1,
Bar = 2,
Baz = 3
};
Then
myEnum myE = myEnum.Foo; /* Default! */
myE = (myEnum)Enum.Parse(myE.GetType(), "Baz");
/* Now, myE should be Baz! */
Console.WriteLine("Enum Selected: {0}", myE.ToString());
The above sample serves to illustrate how to convert a string literal into an enum. I hope this is what you are looking for.

Associating Additional Information with .NET Enum

My question is best illustrated with an example.
Suppose I have the enum:
public enum ArrowDirection
{
North,
South,
East,
West
}
I want to associate the unit vector corresponding to each direction with that direction. For example I want something that will return (0, 1) for North, (-1, 0) for West, etc. I know in Java you could declare a method inside the enum which could provide that functionality.
My current solution is to have a static method -- inside the class that defines the enum -- that returns a vector corresponding to the passed in ArrowDirection (the method uses a HashTable to accomplish the lookup but that's not really important). This seems... unclean.
Question:
Is there a best-practice solution for storing additional information corresponding to an enum in .NET?

There's a FANTASTIC new way to do this in C# 3.0. The key is this beautiful fact: Enums can have extension methods! So, here's what you can do:
public enum ArrowDirection
{
North,
South,
East,
West
}
public static class ArrowDirectionExtensions
{
public static UnitVector UnitVector(this ArrowDirection self)
{
// Replace this with a dictionary or whatever you want ... you get the idea
switch(self)
{
case ArrowDirection.North:
return new UnitVector(0, 1);
case ArrowDirection.South:
return new UnitVector(0, -1);
case ArrowDirection.East:
return new UnitVector(1, 0);
case ArrowDirection.West:
return new UnitVector(-1, 0);
default:
return null;
}
}
}
Now, you can do this:
var unitVector = ArrowDirection.North.UnitVector();
Sweet! I only found this out about a month ago, but it is a very nice consequence of the new C# 3.0 features.
Here's another example on my blog.

I've blogged about it here.
Try out something like this with Attributes.
public enum Status {
[Status(Description = "Not Available")]
Not_Available = 1,
[Status(Description = "Available For Game")]
Available_For_Game = 2,
[Status(Description = "Available For Discussion")]
Available_For_Discussion = 3,
}
public class StatusEnumInfo {
private static StatusAttribute[] edesc;
public static String GetDescription(object e)
{
System.Reflection.FieldInfo f = e.GetType().GetField(e.ToString());
StatusEnumInfo.edesc = f.GetCustomAttributes(typeof(StatusAttribute), false) as StatusAttribute[];
if (StatusEnumInfo.edesc != null && StatusEnumInfo.edesc.Length == 1)
return StatusEnumInfo.edesc[0].Description;
else
return String.Empty;
}
public static object GetEnumFromDesc(Type t, string desc)
{
Array x = Enum.GetValues(t);
foreach (object o in x) {
if (GetDescription(o).Equals(desc)) {
return o;
}
} return String.Empty;
}
}
public class StatusAttribute : Attribute {
public String Description { get; set; }
}
public class Implemenation {
public void Run()
{
Status statusEnum = (Status)StatusEnumInfo.GetEnumFromDesc(typeof(Status), "Not Available");
String statusString = StatusEnumInfo.GetDescription(Status.Available_For_Discussion);
}
}
Instead of Description, use your custom Property

using System.ComponentModel;
using System.Reflection;
public enum ArrowDirection
{
[Description("Northwards")]
North,
[Description("Southwards")]
South,
[Description("Eastwards")]
East,
[Description("Westwards")]
West
}
...
Create an extension method to get a list of descriptions:
public static class Enum<T> where T : struct
{
/// <summary>
/// Gets a collection of the enum value descriptions.
/// </summary>
/// <returns></returns>
public static IList<string> GetDescriptions()
{
List<string> descriptions = new List<string>();
foreach (object enumValue in Enum<T>.GetValues())
{
descriptions.Add(((Enum)enumValue).ToDescription());
}
return descriptions;
}
}

One thing you could look at is the "Type-Safe Enum" pattern. This allows you to create an enum that is actually a full-fledged static object, which can have methods/properties/etc..
http://www.javacamp.org/designPattern/enum.html
Joshua Bloch talks about this pattern in his book "Effective Java." I've used it in a lot of different situations, and I actually prefer it over plain enums. (It's language-agnostic - it works in Java, C#, or pretty much any OO language).

Your static method approach seems quite clean to me. You encapsulate both the enum and the static method within the same class. Changes to the enum are centralised within that single class.
Adding a method to the enumeration (as per Java) seems to add complexity to something that is really a very simple concept.
The attribute based approach is interesting, but once again seems to overcomplicate things when compared to a static method.