Question

Is there any penalty, such that you should only set them as nullable when you really need it?

Thanks

Answer 1

Various reasons:

• History: Nullable<T> didn’t exist until .NET 2.0, and it can’t break existing code – especially with the different boxing rules for Nullable<T>
• Meaning: if I want an int, I might not want it to be nullable… I want it to be an int, and I don’t want to have to check-for/handle nulls
• Space: it adds extra cost to each struct… in particular, imagine a byte[], and now consider if byte was nullable – lots of extra overhead; *plus it would stop you doing blits etc*

• Performance: Nullable<T> adds lots of extra penalties; in particular lots of hidden calls to .HasValue and .Value / .GetValueOrDefault(); this is shown in particular in the “lifted operators” – i.e. x + y becomes something like below, which adds up for tight loops etc:

  (x.HasValue && y.HasValue) ? (x.GetValueOrDefault() + y.GetValueOrDefault()) : null

Likewise, x == y has to check:

• if both null => true
• if one null => false
• otherwise use == on GetValueOrDefault() of each

lots of overhead….