Func & Action:generic delegate is a cool feature introduced with .NET 3.5. We will look at Func & Action in this short article. But let's start with .NET 1.1.
For instance, take a look a tutorial from C# 1.1 or 2.0, the tutorial on how to use the lambda operator. In that tutorial, we wrote a method that would take a delegate and fold it across the rest of the arguments to the function. It looked like this
public delegate int FoldIntDelegate(int a, int b);
public int Fold(FoldIntDelegate fid, params int[] list)
{
int result = 1;
foreach (int i in list)
result = fid(result, i);
return result;
}
That first line is the line that I'm complaining about - the line I'd like to get rid of. Well, guess what? we can! There are a whole bunch of basic delegate declaration in the System name-space that cover almost all of the common delegate declaration cases by using generics. For instance, that Fold method could have been written like this:
public int Fold(Func
{
int result = 1;
foreach (int i in list)
result = fid(result, i);
return result;
}
The Funcs
The Funcs are the delegate declaration for delegates that return a value, and were first introduced in .NET 3.5. We have already seen one, the two argument Func. But there are Func declarations for everything from no arguments to 4 arguments:
Func(TResult)
Func(T1, TResult)
Func(T1, T2, TResult)
Func(T1, T2, T3, TResult)
Func(T1, T2, T3, T4, TResult)
So if you need more than 4 arguments, you have to make your own declaration. But most of the time, you don't, and so this covers many of the common signatures.
what if I don't want to return a value? Well, don't worry, that is here too:
The Actions
The Actions are the delegate declarations to use when your delegate doesn't return a value. Again, there are Actions for everything from zero to 4 arguments. And just as a note, the zero argument Action is not actually a generic delegate - cause there is no need for it to be (there are no types to deal with). The single argument Action was introduced in .NET 2, and the rest of them were added in .NET 3.5.
Action()
Action(T1)
Action(T1, T2)
Action(T1, T2, T3)
Action(T1, T2, T3, T4)
So, I think we got some idea about the Fun & Action generic delegate. Now see how I am using the above Fold function.
class Program
{
static void Main(string[] args)
{
var aa = new int[] { 1, 2, 3, 4 };
var a12 = Fold(ABC, aa);
}
public static int Fold(Func
{
int result = 1;
foreach (int i in list)
result = fid(result, i);
return result;
}
static int ABC(int i1, int i2)
{
return i1 * i2;
}
}
Enjoy:)...
