Question

I wanted to ask what is the idea behind the fact that System.String doesn’t contain parameterless constructor.

Because of this you cannot use this type when there is new() constraint.

UPDATE

Why do you think that new string() is useless and e.g. new int() is not useless. I really cannot see the difference. I really would like to be able to use a new() constraint on string, since what I’m expecting is String.Empty.

UPDATE2

I know that int is a value type and all value types have default parameterless constructor.
I was referring to @John Saunders answer (and similar answers) that were stating that saying new String() basically doesn’t do anything useful. So if new String() doesn’t mean anything useful what is so useful about new int()? I also understand that it is important for value types to have default parameterless constructors. What is more I think that it would be really nice for string to have a default parameterless constructor. Lack of a parameterless constructor means for me that an object simply cannot exist without a parameter that will initialize it. In my opinion string doesn’t need any parameter because it could be empty. I asked this question because I wanted to know if there is some important reason for string not having parameterless constructor or it’s just design or sth else.

UPDATE3

I guess it will be the last update since it looks more like a blog post than a question. In java strings are also immutable and new String() is perfectly legal. However, documentation for parameterless constructor says:

Initializes a newly created String
object so that it represents an empty
character sequence. Note that use of
this constructor is unnecessary since
Strings are immutable.

UPDATE4

Ok, last update 😉 I have to agree with John Saunders. I was using code that had new() constraint and it worked nicely for custom classes. Then, my colleague need to change the code for ints and it was ok. Then change it for string and we had a problem. When I now think about it I guess the code we are using needs to be changed to reflect that we need scalar types not classes that have parameterless constructor. All that said, I still think it’s a bit inconsisent that you can write new int() and you are unable to write new string() (yes, I understand that int is a value type ;)). Thanks for all your answers!

Thanks in advance for help.

Answer 1

If you could use

string s = new string();

What would you do with it? Strings are immutable.

---

Some readers have thought I was saying that a parameterless string constructor would be useless. That’s not what I meant. I meant that the empty string created from such a constructor would be useless in the rest of the code.

Keep in mind what the OP said he wanted to do:

public void SomeMethod<T>() where T : new()
{
    var t = new T();
    // Do _what_ now?
}

// Call:
SomeMethod<string>();

I don’t see what you could do with t after it was constructed.