Null-Removing Function

[TonyValenti]

I would like to create an Enumerable extension method, WhereIsNotNull, that will filter an enumerable to contain only non-null entries and return an enumerable with a non-null type.

Ie.:

WhereIsNotNull( IEnumerable<Person?> ) => IEnumerable<Person>
WhereIsNotNull( IEnumerable<int?> ) => IEnumerable<int>

Is there a way to declare constraints in such a way to enable this (ie, where T : nullable) or will I need two implementations: one for classes and one for structs?

[333fred]

You will need two implementations.

[333fred]

No need to resume that debate - but I do have to note this is the 3rd or 4th such question that was raised recently.

I'll be honest Tahir: this wording implies that you want to resume the debate. We get it. No one on the ldm has said we would have designed nullability this way if we were restarting the language. But we aren't restarting the language, and subtle digs like this just make me less inclined to engage with you in other issues.

[TahirAhmadov]

No I don't. I wrote everything there was to write about it. It wasn't meant as a subtle dig, either - just pointing something out.
Again, I'm not going to continue that topic here or anywhere else.

[TonyValenti]

I'm curious - although it may not be possible with C#, using IL, would that be possible?

[HaloFour]

@TonyValenti

I'm curious - although it may not be possible with C#, using IL, would that be possible?

No, the limitation originates at the bytecode and metadata level. The problem is that with NRTs IEnumerable<T?> is IEnumerable<T> and with NVTs IEnumerable<T?> is really IEnumerable<Nullable<T>> so you end up with incompatible method signatures and require different IL to work with, and generics in the runtime is not designed to work like that.

[TonyValenti]

@HaloFour Thanks for the clarification. That's what I thought but I wasn't sure.