Null out parameters in C#?

Question

After reading on stackoverflow that in the case of checking the format of a DateTime you should use DateTime.TryParse. After trying some regex expressions they seem to get l

Answer 1

No. You can't get rid of the variable but you shouldn't get a compiler warning either.

Passing a variable as out is "using" the variable. The compiler will not issue a warning because of that.

Answer 2

TryParse is a better option. Its just a variable that is wasted. Other options include using the Convert.ToDateTime() within a try-catch block. But again that would not be efficient because try-catch blocks are meant to be heavy. The next option is regex. This is a better solution. I guess this gives you the result instantly than compared to the others.

You can very well wrap the method like Kim Gräsman said...

Answer 3

With C#7.0 (since August 2016) you can use the out var construct, and then just ignore the new var in subsequent code.

bool success = DateTime.TryParse(value, out var result);

If you truly do not care about the value of the result, use discards:

bool success = DateTime.TryParse(value, out _);

Answer 4

Nope. I'd wrap it in a method somewhere to keep the noise out of the main flow:

  bool IsValidDate(string value)
  {
     DateTime result;
     return DateTime.TryParse(value, out result); //result is stored, but you only care about the return value of TryParse()
  }

Answer 5

If you are using .NET 3 and above, you could always create an Extension method?

public static bool IsValidDate(this string value)
{
  DateTime date = DateTime.Null;
  return DateTime.TryParse(value, out date);
}

[Edited to rename the method name to a more appropriate one]

Answer 6

I'm not suggesting you actually do this, but you could use a single helper class to make this easy for all out parameters:

public static class OutHelper<T>
{
    [ThreadStatic]
    public static T Ignored;
}

Then you can call:

if (DateTime.TryParse(text, out OutHelper<DateTime>.Ignored))

It's horrible, uses a public mutable field, and if your application is also executing with some malicious code, it gives that code access to the last value you've parsed... but it should work :)