How can I make a class in C# that I can initialize just like a string?

Question

I want to be able to initialize a class just like I initialize a string:

string str = "hello";
MyClass class = "hello";

I really don't know what exactly string str = "hello"; does. I assume "hello" gets translated by the compiler into new System.String("hello"); but I'm not sure. Maybe is just not possible or maybe I'm missing something very elemental; if that's the case excuse my ignorance :). What I'm trying to make is a class that works just like a string but stores the string in a file automatically.

Ok, here's my code after reading you answers:

class StringOnFile
{
    private static string Extension = ".htm";
    private string _FullPath;
    public bool Preserve = false;

    public string FullPath
    {
        get
        {
            return _FullPath;
        }
    }

    public static implicit operator StringOnFile(string value)
    {
        StringOnFile This = new StringOnFile();
        int path = 0;

        do{
            path++;
            This._FullPath = Path.GetFullPath(path.ToString() + Extension);
        } 
        while(File.Exists(This._FullPath));

        using (StreamWriter sw = File.CreateText(This._FullPath))
        {
            sw.Write(value);
        }

        return This;
    }

    public static implicit operator string(StringOnFile stringOnFile)
    {
        using (StreamReader sr = File.OpenText(stringOnFile._FullPath))
        {
            return sr.ReadToEnd();
        }
    }

    ~StringOnFile()
    {
        if(!Preserve) File.Delete(FullPath);
    }
}

What do you think?

Answer 1

You need to implement implicity conversion from string http://msdn.microsoft.com/en-us/library/z5z9kes2(VS.71).aspx

Answer 2

Well, you can create an implicit conversion from string to your type... but I would personally rarely do so. One example of a class that does is XNamespace from LINQ to XML. Does your class really just have a string member? If so, maybe it's suitable. Or maybe it only has a string and some other fields which can usually be defaulted... but in most cases, I wouldn't expect a conversion from string to be appropriate.

To put it another way: should your users really think of your class in exactly the same way as a string? Is it effectively a wrapper around a string? If you could give us more details, we could give more advice.

And no, the compiler doesn't translate "hello" into new System.String("hello") - that would just cause a recursive problem, of course, as well as breaking interning. IL has direct support for string constants, which the C# compiler uses.

Answer 3

Try the following

class MyClass {
    public static implicit operator MyClass(string value) {
        // Custom logic here 
        return new MyClass();
    }
}

void Example() {
  MyClass v1 = "data";
}

This will get the end result you are looking for. However I would advise against this approach. There are several pitfalls with implicit conversions that you will eventually run into. Much better to just have a constructor which takes the string