Async Validation via Sequence is Failing.

I ran into this today and thought is was my dummy self 😉

Here’s a repro test that shows turning a Success<string, Task<int>> into a Task<Fail<string, int>> where I fully expect Task<Success<string,int>>.

[Fact]
async Task async_validation_via_sequence()
{
    Task<Validation<string, int>> validation = 
        Success<string, int>(1)
        .Map(x => (x * 2).AsTask())
        .Sequence();

    var result = await validation;
    
    Assert.False(result.IsFail);
}

[TysonMN]

Indeed. Here is a slightly shorter MWE.

[Fact]
public async Task ValidationTaskSequence_Success_IsSuccessful()
{
    Task<Validation<string, int>> validation =
        Success<string, Task<int>>(1.AsTask())
        .Sequence();

    var result = await validation;

    Assert.True(result.IsSuccess);
}

[mario-d-s]

@louthy may I ask why this issue was just closed without any solution/workaround? Should we watch #876 instead?

In the meantime, the workaround with Match (actually MatchAsync) that @trbngr mentioned looks like this:

[Fact]
public async Task ValidationTaskSequence_Success_IsSuccessful()
{
    Task<Validation<string, int>> validation =
        Success<string, Task<int>>(1.AsTask())
        .MatchAsync(
            async value => Success<string, int>(await value),
            Validation<string, int>.Fail);

    var result = await validation;

    Assert.True(result.IsSuccess);
}