Nuno Silva

I want one of these without reflection, please!

Some while ago, i saw the following code in a project i’m working:

string[] a = (string[])Array.CreateInstance(typeof(string), 10);

And then i became shocked… I called him every name in the book. And why? Because the complication above could be replaced simply by:

string[] a = new string[10];

And there are 2 reasons:

First: The IL generated by the CreateInstance is much more complex than the IL generated by the new operator:

Create Instance IL:

IL_0000: ldtoken [mscorlib]System.String
IL_0005: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_000a: ldc.i4.s 10
IL_000c: call class [mscorlib]System.Array [mscorlib]System.Array::CreateInstance(class [mscorlib]System.Type,
int32)

new operator IL:

IL_0011: castclass string[]
IL_0016: stloc.0
IL_0017: ldc.i4.s 10
IL_0019: newarr [mscorlib]System.String

Second: because the CreateInstance uses reflection and, because of that, the operation is much more slow. Here are the times, in Miliseconds, for 1 million iterations of each operation:

CreateInstance: 406,2422 ms
New: 31,2494 ms

Has you can see, reflection is very expensive. In this case, just the line of code with CreateInstance is 13 times more expensive then the one with the new operator.

So, be careful where and when you use reflection. The bad use of it can result in a performance break of your application.

Random Posts

• Orion’s Belt Tasks
• Two classics
• Recursive operator == because of a null
• 10,000 BC
• Platinum arrives to PS3