if condition with nullable

Question

There is a lot of syntax sugar with Nullable<T> like those:

int? parsed to Nullable<int>

int? x = null
   if (x != null) // Parsed to if (x.HasValue)

x = 56; // Parsed to x.Value = 56;

And more.

Why if condition with Nullable doesn't work?

if (x)
{} 

It gets Complier error saying can't convert Nullable<bool> to bool.
Why it's not being parsed to if (x.HasValue && x.Value == true) or something similar?

It's the most obvious usage for Nullable<bool>

Answer 1

It's the most obvious usage for Nullable<bool>

Your "obvious" behaviour leads to many inobvious behaviours.

If

if(x)

is treated as false when x is null, then what should happen to

if(!x)

? !x is also null when x is null, and therefore will be treated as false also! Does it not seem strange that you cannot reverse the behaviour of a conditional with an inversion?

What about

if (x | !x)

Surely that should always be true, but if x is null then the whole expression is null, and therefore false.

It is better to avoid these inobvious situations by simply making them all illegal. C# is a "make the user say what they mean unambiguously" language.

I believe that VB has the behaviour you want. You might consider switching to VB if this is the sort of thing you like.

Answer 2

Simply put, it fails to compile because the specification says it should - an if condition requires a boolean-expression - and an expression of type Nullable<bool> isn't a boolean-expression:

A boolean-expression is an expression that yields a result of type bool; either directly or through application of operator true in certain contexts as specified in the following.

However, it's easy to work round:

if (x.GetValueOrDefault())
{
}

Or to possibly be clearer:

if (x ?? false)
{
}

The latter approach is useful as it means you can easily change the behaviour if x is null, just by changing it to x ?? true.