What is the equivalent of FromCanceled(CancellationToken) in .NET 4.5?

I want to achieve something similar to this in .NET 4.5

public virtual Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
    if (!cancellationToken.IsCancellationRequested)
    {
        return BeginEndWriteAsync(buffer, offset, count);
    }

    return Task.FromCancellation(cancellationToken);
}

Task.FromCanceled(CancellationToken) method is available in .NET 8.

I would like to know its equivalent in .NET 4.5.

>Solution :

In .NET 4.5, there isn’t a direct equivalent of the Task.FromCanceled(CancellationToken) method available in .NET 8. However, you can achieve similar behavior by creating a canceled task manually.

Here’s how you can create a canceled task in .NET 4.5:

using System;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
    public static Task CreateCanceledTask(CancellationToken cancellationToken)
    {
        if (cancellationToken.IsCancellationRequested)
        {
            // Create a canceled task with the specified cancellation token.
            var tcs = new TaskCompletionSource<object>();
            tcs.SetCanceled();
            return tcs.Task;
        }
        else
        {
            // Return a non-canceled task.
            return Task.FromResult<object>(null);
        }
    }

    public static async Task Main()
    {
        var cancellationToken = new CancellationToken(/* true or false */);
        var task = CreateCanceledTask(cancellationToken);

        try
        {
            await task;
        }
        catch (TaskCanceledException)
        {
            Console.WriteLine("Task was canceled.");
        }
    }
}

In the CreateCanceledTask method:

If the cancellation token is requested (i.e., cancellation is needed), we create a canceled task using TaskCompletionSource and set it as canceled.
Otherwise, we return a non-canceled task using Task.FromResult.
Remember to replace the /* true or false */ comment with your actual cancellation condition (whether you want the task to be canceled or not).

This approach allows you to mimic the behavior of Task.FromCanceled(CancellationToken) in .NET 4.5