System.String Type in C#

Question

I know that it may sound like a weird question but this has been going on in my mind for a while.

I know that the System.String type in C# is actually a class with a constructor that has a character array parameter. For example the following code is legal and causes no error:

System.String s = new System.String("Hello".toCharArray());

My question is that what makes is possible for the System.String class to accept an array of characters simply this way:

System.String s = "Hello";

Answer 1

When you call:

System.String s = new System.String("Hello".toCharArray());

You are explicitly invoking a constructor

When you write:

string foo = "bar";

An IL instruction (Ldstr) pushes a new object reference to that string literal. It's not the same as calling a constructor.

Answer 2

This is possible because the C# language specifies that string literals are possible (see §2.4.4.5 String literals). The C# compiler and CIL/CLR have good support for how these literals are used, e.g. with the ldstr opcode.

There is no support for including such literals for your own custom types.

Answer 3

Strings are kind of a special clr type. They are the only immutable reference type.

Here are several things which may help you to understand string type:

 var a = "Hello";
 var b = new String("Hello".ToCharArray());
 var c = String.Intern(b); // 'interns' the string...
 var equalsString = a == b;  // true
 var equalsObj =    (object)a == (object)b; // false
 var equalsInterned =    (object)a == (object)c; // true !!

 a[0] = 't'; // not valid, because a string is immutable. Instead, do it this way:
 var array = b.ToArray();
 array[0] = 't';
 a = new String(array); // a is now "tello"