Is there a better way to express a parameterless lambda than () =>?

Question

The () seems silly. is there a better way?

For example:

ExternalId.IfNotNullDo(() => ExternalId = ExternalId.Trim());

Answer 1

Sort of! There is a new idiom in town, that is nice and may help you in some cases. It is not fully what you want, but sometimes I think you will like it.

Since underscore ("_") is a valid C# identifier, it is becoming a common idiom to use it as a parameter name to a lambda in cases where you plan to ignore the parameter anyway. If other coders are aware of the idiom, they will know immediately that the parameter is irrelevant.

For example:

ExternalId.IfNotNullDo( _ => ExternalId=ExternalId.Trim());

Easy to type, conveys your intent, and easier on the eyes as well.

Of course, if you're passing your lambda to something that expects an expression tree, this may not work, because now you're passing a one-parameter lambda instead of a no-parameter lambda.

But for many cases, it is a nice solution.

Answer 2

For a lambda, no: you need () =>

Is it for a delegate or an expression? For delegates, another option is delegate {...}. This may or may not be desirable, depending on the scenario. It is more keys, certainly...

In some cases (not this one) you can use a target method directly - i.e.

ExternalId.IfNotNullDo(SomeMethod);

Answer 3

Essentially what you're looking for is the inverse of the ?? null coalescing operator (which is called Nullable<T>.GetValueOrDefault() under the covers) - problem is C# doesn't provide a neat OOTB answer.

Don't know exactly what you're doing but as you are doing:

ExternalId.IfNotNullDo(()=>ExternalId=ExternalId.Trim());

you might also find a use for:

class NullExtensions
{
    public T DefaultOr<T>( this T that, Func<T> transform)
    {
        return that!=default(T) ? transform(that) : default(T);
    }
}

which would enable:

var result = input.DefaultOr( _ => _.Trim());

(in general, I'd be trying to steer away from reusing / mutating variables as you seem to be doing and instead going in an Introduce Explaining Variable / Split Temporary Variable direction i.e., use a new variable rather than value = value.DefaultOr( _ => _.Trim());)

Answer 4

No, there isn't. Lambda expressions are optimised (in terms of syntax) for the single parameter case.

I know that the C# team feels your pain, and have tried to find an alternative. Whether there ever will be one or not is a different matter.