Nice C# idiom for parameterless lambdas

The C# syntax for a lambda with no parameters is kind of ugly:

public static void SomeMethod(Person person)
{
   Console.WriteLine( ()=> person.FirstName );
   // The ugly syntax is: ()=> person.FirstName
}

However, there is a nice, relatively new idiom springing up that makes it a little better. The idiom is to use underscore (“_”) as the parameter. Underscore is a valid name for an identifier in C#.

The convention is that, as the idiom becomes more widespread, people reading your code will know that you would never name a meaningful parameter with underscore, so therefore they know you’re going to ignore the parameter. So in effect, they understand that the intent is a parameterless lambda.

As a result, you wind up with this:

public static void SomeMethod(Person person)
{
   Console.WriteLine( _=> person.FirstName );
}

There’s another reason this idiom is appealing: its harmony with F#. F# is a language on the rise, and we’re likely to see more and more projects which have a mix of F# and C#. In F# (and many other functional languages as well), there is a key language feature called pattern matching. At an over-simplified level, it is like a case statement. And there is syntax for a “wild card” pattern that matches everything. That syntax happens to be underscore! More specifically, when used in an F# pattern match, the underscore means, “Match whatever input I’m being compared to, and I don’t plan to use the value of that input in the expression I’m about to execute.” Which is almost exactly the same meaning we’re trying to express here.

Of course, you’ll have to decide for yourself whether you like the underscore or the original ()=> syntax better. Clearly that’s a subjective matter.

Also, beware that sometimes the two aren’t interchangeable, depending on what you’re doing with the lambda. If you use the underscore idiom, then of course you really do have a single-parameter lambda. If you’re passing the lambda to a method that is going to require a zero-parameter lambda (because it takes an expression tree from the lambda or something like that), then the underscore idiom is not going to work.

You can find more info here.