Wed, December 22, 2004, 05:09 AM under
MobileAndEmbedded
A disclaimer up front: This is by no means a tutorial or even my original work on Generics. The subject has been discussed in depth ever since it was announced as part of Whidbey. Given that generics were not available in the Compact Framework in previous releases and I
did say I would talk about them a bit, here goes some code for CF from the
November CTP (tested in the emulator):
I bet 90% of the mileage on generics use will come out of using the classes in the framework and specifically the System.Collections.Generic namespace. An example is this:
' VB - consuming built-in collections
Dim s As New System.Collections.Generic.Stack(Of Int32)
s.Push(5) 'no boxing
s.Push(6)
's.Push("invalid") 'will not compile :-) Dim tot As Int32 = s.Pop() + s.Pop() 'no cast
// C# - consuming built-in collections
System.Collections.Generic.Stack<int> s;
s = new Stack<int>();
s.Push(5); //no boxing
s.Push(6);
//s.Push("invalid"); //will not compile :-) int tot = s.Pop() + s.Pop(); //no cast
However, you can create your own generics classes and even structs:
' VB - Declare generic struct
Public Structure MyPoint(Of T)
Dim x As T
Dim y As T
End Structure
// C# - Declare generic struct
public struct MyPoint<T> { T x;
T y;
}
...and of course consume them:
' VB - consume generic struct
Dim mp As New MyPoint(Of Single)
mp.x = 12.3
mp.y = 5
// C# - Consuming own struct
MyPoint<float> mp = new MyPoint<float>();
mp.x = 12.3;
mp.y = 5.2;
Even more useful, you can create generic methods and impose constraints on the types:
'VB - generic method with constraints
Public NotInheritable Class MyMath
Private Sub New()
End Sub
Public Shared Function Min(Of T As IComparable)(ByVal a As T, ByVal b As T) As T
If a.CompareTo(b) < 0 Then 'no casting + intellisense help
Return a
End If
Return b
End Function
End Class
// C# - generic method with constraints
public static class MyMath { //Min with constraints
public static T Min<T>(T a, T b) where T : IComparable { if (a.CompareTo(b) < 0) {//no casting + intellisense help return a;
}
return b;
}
}
' VB - Consume generic method
Dim m As Int32 = MyMath.Min(6, 8)
// C# - Consume generic method
int m = MyMath.Min(6, 8);
I have only scratched the surface here, if you want to know more about Generics I encourage you to go searching. I can recommend these articles: [
1,
2]
UPDATE (7 Jan 05): Roman Batoukov has
the implementation details
UPDATE (26 Jan 05): Nazim Lala has the details on
reflection with generics