How to work with IEnumerable and the yield keyword? yield == Error "The body cannot be an iterator block because Result<IEnumerable<T>, Error> is not an iterator

[jeffward01]

I feel like im doing something wrong... I know you want to wrap your Methods in Result<T, E> so that you know if they failed or succeeded, but when it comes to IEnumerable specifically using the yield keyword - does it work differently?

I searched all of the issues, and code, and did not find anything that could answer my question:

    protected override Result<IEnumerable<TEntity>, Error> ReplaceRange(
        IEnumerable<TEntity> entities,
        PersistOptions persistOptions)
    {
        var arrayOfEntities = entities.ToArray();
        foreach (var entity in arrayOfEntities)
        {
            entity.AsMaybe()
                .ToResultWithErrorCode(DomainErrors.NullOrEmpty.EntityWasNull)
                .Ensure(_ => entity.HasPrimaryKey(), DomainErrors.NotFound.MissingPrimaryKey)
                .Tap(this.AttachEntity);
        }

        this.CommitIfAllowed(persistOptions);

        foreach (var entity in arrayOfEntities)
        {
            yield return entity;
        }

The examples I have seen show something like: IEnumerable<Result<TEntity, Error>> -- but when I look at that, I see this:

• There is no result wrapper on the IEnumerable<>, so I don't know if the Method call was a success or fail
• I only see Result<TEntity, Error> - so I can see if each individual iterator result was a success or failure

I asked a similar question to this regarding IAsyncEnumerable here

I'm relatively new to proper Functional programming, in the past I have just used Maybe<>, and now im embracing it more.

There must be something im missing with the usage of the yield keyword

Question

What is the proper way to return IEnumerable from a method using yield to achieve a continuous returned data-stream?

[jeffward01]

Also, if anyone has suggestions on how I can improve my code and avoid the IEnumerator has multiple enumerations error - I would appreciate it!

[jeffward01]

Here: #354

I see you can perform a workaround of:

return Result.Success<IEnumerable<TEntity>, Error>(arrayOfEntities);

So now it compiles like this:

   // this is valid code, no errors (I have not testing it yet)
    protected override Result<IEnumerable<TEntity>, Error> ReplaceRange(
        IEnumerable<TEntity> entities,
        PersistOptions persistOptions)
    {
        var arrayOfEntities = entities.ToArray();
        foreach (var entity in arrayOfEntities)
        {
            entity.AsMaybe()
                .ToResultWithErrorCode(DomainErrors.NullOrEmpty.EntityWasNull)
                .Ensure(_ => entity.HasPrimaryKey(), DomainErrors.NotFound.MissingPrimaryKey)
                .Tap(this.AttachEntity);
        }

        this.CommitIfAllowed(persistOptions);

        return Result.Success<IEnumerable<TEntity>, Error>(arrayOfEntities);
    }

But now I have lost the power of the keyword yield and can no longer return a datastream of continue events?

Is it possible to use yield with the Result<T, E> type?