Visual Studio Hacks

Examine the IL Generated by Your Code #63

Chapter 7, Help and Research

|

247

HACK

.locals init ([0] string s,

[1] string CS$00000003$00000000)

IL_0000: ldsfld string [mscorlib]System.String::Empty

IL_0005: stloc.0

IL_0006: ldloc.0

IL_0007: stloc.1

IL_0008: br.s IL_000a

IL_000a: ldloc.1

IL_000b: ret

} // end of method Class1::GetBlankString2

At first glance, IL is a little confusing, and I don’t plan on trying to teach you

everything about IL in this hack. But looking at these two simple examples,

you will see one major difference. In the first method, you will see that the

IL_0000: line contains this line of code:

IL_0000: ldstr ""

And on the same line in the second method is this line of code:

IL_0000: ldsfld string [mscorlib]System.String::Empty

To understand these two lines, you first need to understand what the com-

mands

ldstr and ldsfld actually do. The IL command ldstr creates a new

string (or most likely pulls it from the string pool). The IL command

ldsfld

loads a static field from a class. Using the first string method creates a new

string object, whereas the second method simply loads the value of a static

field. To be sure, this is a tiny difference in these two procedures. You would

probably never notice the performance difference between these two meth-

ods, even if you ran the process hundreds of times. But understanding the

difference and how the .NET Framework works is what’s important. ...