Is there ever a reason to use goto in modern .NET

Question

I just found this code in reflector in the .NET base libraries...

    if (this._PasswordStrengthRegularExpression != null)
    {
        this._PasswordStrengthRegularExpression = this._PasswordStrengthRegularExpression.Trim();
        if (this._PasswordStrengthRegularExpression.Length == 0)
        {
            goto Label_016C;
        }
        try
        {
            new Regex(this._PasswordStrengthRegularExpression);
            goto Label_016C;
        }
        catch (ArgumentException exception)
        {
            throw new ProviderException(exception.Message, exception);
        }
    }
    this._PasswordStrengthRegularExpression = string.Empty;
Label_016C:
    ... //Other stuff

I've heard all of the "thou shalt not use goto on fear of exile to hell for eternity" spiel. I always held MS coders in fairly high regard and while I may not have agreed with all of their decisions, I always respected their reasoning.

So - is there a good reason for code like this that I'm missing? Was this code extract just put together by an inept developer? or is .NET reflector returning inaccurate code?

I'm hoping there is a good reason, and I'm just blindly missing it.

Thanks for everyone's input

Answer 1

goto is perfectly valid for cleanup stuff in languages like C at least, where it somewhat simulates the notion of exceptions. I'm sure that .NET has better ways of handling stuff like this, so goto is just obsolete and error prone.

Answer 2

There is one valid case - when you are trying to simulate a recursive procedure call and return in a non-recursive code, or do something similar (this kind of requirement also occurs in a Prolog interpreter). But in general, unless you are doing something requiring micro-optimization like a chess program or language interpreter, much better to just use the regular procedure stack and use function/procedure calls.

Answer 3

Thou shalt not look at reflector code.

Although if you ever look at disassembled IL, you'll see gotos all over the place. In essence, all of the loops and other control constructs we use are converted to gotos anyway, it's just that by turning them into constructs in our code, it becomes more readable and easier to maintain.

I don't think the code you posted would be a good place to use goto, by the way, and I struggle to think of one.

Answer 4

Goto's are frequently useful when writing parsers and lexers.

Answer 5

No, there's no good reason to use goto. I last coded a goto statement in 1981, and I haven't missed that particular construct since.

Answer 6

Reflector is not perfect. The actual code of this method is available from the Reference Source. It is located in ndp\fx\src\xsp\system\web\security\admembershipprovider.cs:

        if( passwordStrengthRegularExpression != null )
        { 
            passwordStrengthRegularExpression = passwordStrengthRegularExpression.Trim();
            if( passwordStrengthRegularExpression.Length != 0 ) 
            { 
                try
                { 
                    Regex regex = new Regex( passwordStrengthRegularExpression );
                }
                catch( ArgumentException e )
                { 
                    throw new ProviderException( e.Message, e );
                } 
            } 
        }
        else 
        {
            passwordStrengthRegularExpression = string.Empty;
        }

Note how it failed to detect the last else clause and compensated for it with a goto. It is almost certainly tripped-up by the try/catch blocks inside the if() statements.

Clearly you'll want to favor the actual source code instead of the decompiled version. The comments in themselves are quite helpful and you can count on the source being accurate. Well, mostly accurate, there's some minor damage from a buggy post-processing tool that removed the names of the Microsoft programmers. Identifiers are sometimes replaced by dashes and the code is repeated twice. You can download the source here.