Nullable types

[Stewart Gordon]

"Lionello Lunesu" <lionello at lunesu.remove.com> wrote in message 
news:gdhd0f$g3v$1 at digitalmars.com...
<snip>
> [1] http://delight.sourceforge.net/null.html

It seems that Delight had the same idea as Nice.  Which was first?

I see C# is a bit different - primitive types have nullable variants, but 
classes are always nullable.

Is there any language where you can have multiple levels of nullness? 
Something like Type?? which could represent, along with a Type object or 
lack thereof, a lack of any (Type object or lack thereof).  If that makes 
sense.  (It could be done with pointers in C/C++/D, but that adds levels of 
indirection and requires the programmer to allocate little bits of memory to 
deal with them.)

> [2] 
> http://research.microsoft.com/fsharp/manual/import-interop.aspx#Nullness

This might take a bit of studying to make sense of....

Stewart.

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