Negate the null-coalescing operator

Question

I have a bunch of strings I need to use .Trim() on, but they can be null. It would be much more concise if I could do something like:

string endString = startString !?? startString.Trim();

Basically return the part on the right if the part on the left is NOT null, otherwise just return the null value. I just ended up using the ternary operator, but is there anyway to use the null-coalescing operator for this purpose?

Answer 1

string endString = string.IsNullOrEmpty(startString) ? startString : startString.Trim();

Though I've also gone the route of writing a string extension method called "safeTrim" which does what you're describing in one method instead of having to use this recipe every time. Check out Kevin's respone for the code.

EDIT: wow I had it all kinds of backwards, wrongly named variables and reversed ternary operators, all the more reason to write one extension method and code check it better than I did!

Answer 2

Use

string endString = (startString ?? "").Trim();

This uses an empy string if startString is null. This, however, does not return null when endString is null.

Answer 3

Not to spec: Not that I like it, but you could use:

string endString = (startString ?? String.Empty).Trim();

To spec, better as an Extension method like @Kevin's:

string endString = (startString == null ? null : startString.Trim());

Answer 4

You could create an extension method which returns null when it tries to trim the value.

public String TrimIfNotNull(this string item)
{
   if(String.IsNullOrEmpty(item))
     return item;
   else
    return item.Trim();
}

Note you can't name it Trim because extension methods can't override instance methods.

Answer 5

The following doesn't propagate null but it accepts null as a parameter and returns an empty string in that case.

using Microsoft.VisualBasic;  // you need to add a reference to Microsoft.VisualBasic.dll

    ...
    string endString = Strings.Trim(startString);
    ...

_duck&run...

Answer 6

Create a method such as:

string MyTrim(string a) {
    if (a != null) {
        a = a.Trim();
    }
    return a;
}

Answer 7

As as side note, if you're using .NET 4, there's a new convenient method String.IsNullOrWhiteSpace which you can use.