将foreach语句重构为LINQ

Question

I have been working on a project and I'm actually refactoring some code. I have encountered myself with lots of foreach and if statements, which could be easily replace with LINQ.

But I have this code snippet, that I wonder how I could make it more functional style.

foreach (var notification in notifications)
{
    if (_emailService.SendEmail(notification.Message.Subject, notification.Message.Body, notification.Message.MailTo))
    {
        successNotificationIDs.AddRange(notification.ID);
    }
    else
    {
        errorCount++;
    }
}

The SendEmail method of the EmailService returns a bool. If its execution has been successfully, it will add an IEnumerable of Int to a declared collection (successNotificationsIDs). If not, I will increase the errorCount variable.

Answer 1

To separate the items of a sequence into all of those that pass some predicate and those that didn't, you can use ToLookup . Use your predicate as the selector:

var lookup =  notifications.ToLookup(notification =>
    _emailService.SendEmail(notification.Message.Subject, 
        notification.Message.Body,
        notification.Message.MailTo));

var successfulIDs = lookup[true].SelectMany(notification => notification.ID);
var errorCount = lookup[false].Count();