Document ValueTask default constructor

[pepone]

dotnet-api-docs/xml/System.Threading.Tasks/ValueTask.xml

Line 48 in 892ea13

## Remarks

The behavior of the ValueTask default constructor is not documented, apparently it is equivalent to new ValueTask(Task.CompletedTask)

[glihm]

@pepone hello,

This is not an issue, ValueTask is a structure. So the default constructor is provided by C#. You can't implement it.

    // Default constructor is implicitly defined, it sets all the struct's fields to their default value.
    ValueTask v = new ValueTask();

[pepone]

It will be useful if the documentation tells that a default constructed task is a completed task, equivalent to new ValueTask(Task.CompletedTask). Afaik this info is not provided in ValueTask documentation.

[glihm]

@pepone in that sense you're right and I didn't get you right at the first reading. The documentation might need to be more accurate.

I am just wondering that, the default state of ValueTask can't be an other one. It must be Completed because Fault and Cancel have no sense for a new ValueTask.

[pepone]

We wanted to use default in our product but we decided against it because this was not documented behavior.

[glihm]

We wanted to use default in our product but we decided against it because this was not documented behavior.

We need now to wait maintainers point of view and suggestions. :)

[glihm]

@pepone ,

I was using ValueTask and I was wondering about your question.
I have checked the code, and there are some dev comments about this, look at those:

• For ValueTask

// An instance created with the default ctor (a zero init'd struct) represents a synchronously, successfully completed operation.

• For ValueTask<TResult>

// An instance created with the default ctor (a zero init'd struct) represents a synchronously, successfully completed operation
// with a result of default(TResult).

I do think those comments can be added to the documentation to provide a clear and deterministic information about default initialization of ValueTask. 👍

[glihm]

@carlossanlop what do you thing about the changes? Should we rework them?
Thanks!

[carlossanlop]

Tagging area owners @tarekgh @stephentoub. Do you agree with the text addition @glihm is suggesting for the ValueTask type's remarks?

[tarekgh]

@carlossanlop I think there is already opened PR #4576 for that.