Why can't you destructure to a tuple with only one value?

Question

In C# 7, it's apparently not possible to destructure to a tuple with only one item.

ValueTuple<T1> exists, so it's not because of that.

And backwards compatibility means a Deconstruct method with one argument must also be legal:

public void Deconstruct(out int i)

So why couldn't you write:

var (num) = foo;

Is it simply that there's no sensible use case for this?

Answer 1

My guess: consider the following case:

int num;
(num) = foo;

If foo defines a deconstructor with out int and an implicit int cast operator, it will be ambiguous which should be invoked in this case

It is possible to have a compile error in this specific case while allowing the general case I guess, but since, as you mentioned, there is no use case and the syntax would be confusing, maybe it makes sense to not allow it at all