C#

int foo = null; //Design time/ compile time error : assigning null to non-nullable primative type
int? bar = null; //OK
string baz = null; //OK, string is nullable.
string? quux = null; //Design time / compile time error : string is nullable
Nullable<string> foo1 = null; //Design time/ compile time error : string is nullable
object bar1 = null; //OK: Object nullable
MyClass baz1 = null; //OK: Object nullable as is an object.

keefb wrote:

Personally, I'd stear clear of nullable values where possible, as you will need to perpetually check the value is not null and other types of evil ensue.

vtpdawg wrote:

There are plenty of good uses for Nullable.

vtpdawg wrote:

I don't see how if (val == -1) is much different than if (val == null)

Dictionary <int,string> lookup;

public void SetupLookup()
{
  lookup = new Dictionary <int,string>();
  lookup.Add(-1, "Unkown");
  lookup.Add(0,"Naughty");
  lookup.Add(1, "Nice");
}

//This is the "clean" non-nullable example 
public void string Lookup(int foo)
{
  return lookup[foo];
}

//This is less clean nullable example, for this example the -1 key in the dictionary is not needed.... 
public void string Lookup2(int& foo)
{
  if(foo.HasValue)
    return lookup[foo];
  return "Unknown";
}

vtpdawg wrote:

You mention "rogue nulls hanging around" like they're some loitering punks harassing passerbys

vtpdawg wrote:

null is not something to be feared, the prudent developer should just be in the practice of always considering null when dereferencing objects.

vtpdawg wrote:

Here, null is used as a return for standard deviation if the set to calculate is invalid (e.g. null, empty, or < 2 elements).

vtpdawg wrote:

Here, null is used as a return for standard deviation if the set to calculate is invalid (e.g. null, empty, or < 2 elements).

vtpdawg wrote:

I think I tend to like that better than an out parameter and a boolean return value, and is certainly preferable to returning a valid double in an error case.