Wednesday, September 10, 2014

C# – Shorten null check around foreach loops

This is another blog post filed under “So I can remember this for next time. If it helps you too, great!”

In C#, when looping over a collection where the collection object itself might be null, if the desired behavior is to just loop zero times if the collection object is null, typical code would be:

List<MyType> list = PopulateList(); // Some method that returns a List<MyType>, or null 
if (list != null) 
{ 
  foreach (MyType mt in list) 
  { 
    // Do stuff with mt... 
  }
}

Using the C# null-coalescing operator ??, the above code can be condensed to:

List<MyType> list = PopulateList(); // Some method that returns a List<MyType>, or null
foreach (MyType mt in list ?? Enumerable.Empty<MyType>) 
{ 
  // Do stuff with mt... 
}

In that second example, if list is non-null, then the foreach iterates over it as normal. If list is null, then the foreach iterates over an empty collection -- so zero iterations are performed.

1 comment:

  1. Thankyou!
    ps I think the example is missing parenthesis..

    foreach (MyType mt in list ?? Enumerable.Empty())

    or you get this error

    Operator '??' cannot be applied to operands of type 'List' and 'method group'

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