This print for content only-size & color not accurate 7" X 9-1/4" / casebound / malloy

// Set initial string value.

string s1 = "This is my string.";

Console.WriteLine("s1 = {0}", s1);

// Uppercase s1?

string upperString = s1.ToUpper();

Console.WriteLine("upperString = {0}", upperString);

// Nope! s1 is in the same format!

Console.WriteLine("s1 = {0}", s1);

}

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If you examine the relevant output in Figure 3-12, you can verify that the original string object

(s1) is not uppercased when calling ToUpper(), rather you are returned a copy of the string in a

modified format.

Figure 3-12.

Strings are immutable!

The same law of immutability holds true when you use the C# assignment operator. To illus-

trate, comment out (or delete) any existing code within StringAreImmutable() (to decrease the

amount of generated CIL code) and add the following code statements:

static void StringAreImmutable()

{

string s2 = "My other string";

s2 = "New string value";

}

Now, compile your application and load the assembly into ildasm.exe (again, see Chapter 1). If

you were to double-click the Main() method, you would find the CIL code shown in Figure 3-13.

Figure 3-13.

Assigning a value to a string object results in a new string object.

Although we have yet to examine the low-level details of the Common Intermediate Language

(CIL), do note that the Main() method makes numerous calls to the ldstr (load string) opcode. Sim-

ply put, the ldstr opcode of CIL loads a new string object on the managed heap. The previous

string object that contained the value "My other string." will eventually be garbage collected.

So, what exactly are we to gather from this insight? In a nutshell, the string type can be ineffi-

cient and result in bloated code if misused, especially when performing string concatenation. If you

need to represent basic character data such as a US Social Security number (SSN), first or last

names, or simple string literals used within your application, the string data type is the perfect

choice.

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