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If you think of delegates as being similar to interface definitions for a specific type of method, you can start to see why delegates exist. They allow clients of our delegates to ignore all the details of their implementations - even their names!
Delegates in C# are similar to function pointers in C++, but C# delegates are type safe. You can pass methods as parameters to a delegate to allow the delegate to point to the method. Delegates are used to define callback methods and implement event handling, and they are declared using the “delegate” keyword.
A method is a group of statements that together perform a task. Every C# program has at least one class with a method named Main. To use a method, you need to − Define the method. Call the method.
I was attempting to compare three different ways of passing a delegate to a function in C# -- by lambda, by delegate, and by direct reference. What really surprised me was the direct reference method (i.e. ComputeStringFunctionViaFunc(object[i].ToString)) was six times slower than the other methods. Does anyone know why this is?
The complete code is as below:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.CompilerServices;
namespace FunctionInvocationTest
{
class Program
{
static void Main(string[] args)
{
object[] objectArray = new object[10000000];
for (int i = 0; i < objectArray.Length; ++i) { objectArray[i] = new object(); }
ComputeStringFunction(objectArray[0]);
ComputeStringFunctionViaFunc(objectArray[0].ToString);
ComputeStringFunctionViaFunc(delegate() { return objectArray[0].ToString(); });
ComputeStringFunctionViaFunc(() => objectArray[0].ToString());
System.Diagnostics.Stopwatch s = new System.Diagnostics.Stopwatch();
s.Start();
for (int i = 0; i < objectArray.Length; ++i)
{
ComputeStringFunction(objectArray[i]);
}
s.Stop();
Console.WriteLine(s.Elapsed.TotalMilliseconds);
s.Reset();
s.Start();
for (int i = 0; i < objectArray.Length; ++i)
{
ComputeStringFunctionViaFunc(delegate() { return objectArray[i].ToString(); });
}
s.Stop();
Console.WriteLine(s.Elapsed.TotalMilliseconds);
s.Reset();
s.Start();
for (int i = 0; i < objectArray.Length; ++i)
{
ComputeStringFunctionViaFunc(objectArray[i].ToString);
}
s.Stop();
Console.WriteLine(s.Elapsed.TotalMilliseconds);
s.Reset();
s.Start();
for (int i = 0; i < objectArray.Length; ++i)
{
ComputeStringFunctionViaFunc(() => objectArray[i].ToString());
}
s.Stop();
Console.WriteLine(s.Elapsed.TotalMilliseconds);
Console.ReadLine();
}
[MethodImpl(MethodImplOptions.NoInlining)]
public static void ComputeStringFunction(object stringFunction)
{
}
public static void ComputeStringFunctionViaFunc(Func<string> stringFunction)
{
}
}
}
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