C# 2.0 ?? Operator

Mon Mar 27, 2006 by Mladen Prajdić in net

I saw this operator in use today in a code example. I must say when I figured what it does my geek side went "YES!!!!".
It resembles an old "if" abbreviation:

(condition ? true result : false result);

now what ?? does is a null check same as the SQL Servers Coalesce function. It returns the first non null parameter.

function test(class1 variable)
{
    if (variable == null)
        variable = new class1();
    // equals to
    variable = (variable ?? new class1());
}

I'm starting to use this and giving a "What!?!???" moment when they see it and a "Yes!!" moment when they figure it out to anyone who's going to look at my code from now on. :))

Legacy Comments


Rob Cannon 2006-03-27	re: C# 2.0 ?? Operator I don't think that your two expressions are not the same. if (variable == null) variable = new class1(); At the end of this statement, variable is not null. (variable ?? new class1()); This does not do an assignment and if variable is null before the statment is executed, it will still be null. This can be dangerous if this cause a new class1 to be created every time the expression is evaluated. variable = variable ?? new class1(); This is closer to what you want, but the assignment is made every time (unless the optimizer takes care of that).

mladen 2006-03-28	re: C# 2.0 ?? Operator well it returns the first non null parameter so i guess it's how you program it :)) oh and thanx for the check.... copy paste sometimes sucks :))

Bino 2008-09-05	re: C# 2.0 ?? Operator Coalesce operator can only be used for NULL values? www.codepal.co.in

good 2008-10-13	re: C# 2.0 ?? Operator coooooooooooooooooooolllllllllllll