If / Then - Statements, How can I achieve this functionally speaking? If value == xx, do this, else, do that

[jeffward01]

Hello!

I am just trying to figure out what the functional equivalent of a if and else statement is. I am sure I can create my own extension methods for this, but there must be something in the library that I am not aware of. here is my scenario:

Scenario

I am trying to call a method, the method has (2) overloads:

void MarkForUpdate(DateTime);

void MarkForUpdate<TKey>(TKey, DateTime)
 where TKey : IComparable<TKey>, IEquatable<TKey>;

Key is usually a type of Guid, so all I want to do is perform something like below. Here is how I would do this action the OOP old way of doing things (not-functional):

var _myDateProvider = DateTime.UtcNow;

if (appUserId.IsNullOrDefault())
{
    MarkUpdate(_myDateProvider);
}
else
{
    MarkUpdate(appUserId, _myDateProvider);
}

I would love to achieve this functionally, i'm just not sure of the API methods to do so.

Can anyone provide any suggestions please?

Thanks

[rutkowskit]

There are at least 2 options.

Option 1:

        Result.Success(_myDateProvider)
            .TapIf(appUserId.IsNullOrDefault(), MarkUpdate)
            .TapIf(appUserId.IsNullOrDefault() is false, dp => MarkUpdate(appUserId.Value, dp));

Option 2:

        Result.SuccessIf(appUserId.IsNullOrDefault(), "appUserId not set")            
            .Tap(() => MarkUpdate(_myDateProvider))
            .TapError(() => MarkUpdate(appUserId.Value, _myDateProvider));    

[jeffward01]

Thanks for this! I really appreciate it!

I think that I need to get used to is the Result.Success or the “error (string)” variable.

In OOP it’s just like “if this, then do that” — and in functional, the thought process of using a Result.Success, and even pairing it with an error message seems so foreign to me. Such as I struggle to grasp why “If this, then that” requires an error message, or a success.

Both routes in “if this, then that” are technically a success… but I also understand that functional programming is about 2 routes - success and error.

Thanks for the examples it helps grasp things, hopefully others will appreciate it also