/// <summary>
/// This method implements <see cref="AsyncDataColumn.TryGetValueAsync"/> method.
/// </summary>
/// <returns>A task which will on completion contain <see cref="ResultOrNone{TResult}"/> struct describing the data.</returns>
/// <seealso cref="ResultOrNone{TResult}"/>
/// <remarks>
/// If value reading has already been started by <see cref="ReadBytesAsync(Byte[], Int32, Int32)"/> method and not yet finished, this method will return <see cref="ResultOrNone{TResult}"/> such that its <see cref="ResultOrNone{TResult}.HasResult"/> property is <c>false</c>.
/// </remarks>
public async ValueTask <ResultOrNone <Object> > TryGetValueAsync()
{
Int32 oldState;
ResultOrNone <Object> retVal;
if ((oldState = Interlocked.CompareExchange(ref this._state, READING_WHOLE_VALUE, INITIAL)) > COMPLETE)
{
// Either concurrent/re-entrant attempt, or reading by bytes has started, or faulted
retVal = new ResultOrNone <Object>();
}
else
{
if (oldState == INITIAL)
{
// First-time acquisition
var faulted = true;
try
{
Interlocked.Exchange(ref this._value, await this.PerformReadAsValueAsync());
faulted = false;
}
catch
{
Interlocked.Exchange(ref this._state, FAULTED);
throw;
}
finally
{
if (!faulted)
{
Interlocked.Exchange(ref this._state, COMPLETE);
}
}
}
retVal = this._state == FAULTED ? default : new ResultOrNone <Object>(this._value);
}
return(retVal);
}
/// <summary>
/// Gets the result from <see cref="ResultOrNone{TResult}"/>, or throws it it doesn't have a result.
/// </summary>
/// <typeparam name="T">The type of the result.</typeparam>
/// <param name="resultOrNone">The <see cref="ResultOrNone{TResult}"/>.</param>
/// <returns>The result of this <see cref="ResultOrNone{TResult}"/>, if it has one.</returns>
/// <exception cref="InvalidOperationException">If this <see cref="ResultOrNone{TResult}"/> does not have a result (its <see cref="ResultOrNone{TResult}.HasResult"/> property is <c>false</c>).</exception>
public static T GetResultOrThrow <T>(this ResultOrNone <T> resultOrNone)
{
return(resultOrNone.HasResult ? resultOrNone.Result : throw new InvalidOperationException("Result is not available."));
}