Is there an “opposite” to the null coalescing operator? (…in any language?)

Question

null coalescing translates roughly to return x, unless it is null, in which case return y

I often need return null if x is null, otherwise return x

Answer 1

PowerShell let's you reference properties (but not call methods) on a null reference and it will return null if the instance is null. You can do this at any depth. I had hoped that C# 4's dynamic feature would support this but it does not.

$x = $null
$result = $x.y  # $result is null

$x = New-Object PSObject
$x | Add-Member NoteProperty y 'test'
$result = $x.y  # $result is 'test'

It's not pretty but you could add an extension method that will function the way you describe.

public static TResult SafeGet(this T obj, Func selector) {
    if (obj == null) { return default(TResult); }
    else { return selector(obj); }
}

var myClass = new MyClass();
var result = myClass.SafeGet(x=>x.SomeProp);