Becoming functional: adding Option of T to List when IsSome only

[Bernhard Hiller]

Eventually I decided to start with the functional concept and installed the LanguageExt library (see GitHub - louthy/language-ext: C# functional language extensions - a base class library for functional programming[^] ). In our code base, there is a class which is full of bool TryGet(some parameters, out T result) functions - I want to change them to Option TryGet(some parameters). But then, things start to look ugly at a different level. E.g.

List result = new List();
...
foreach (IIntersectionInfo intersection in intersections)
{
Option angle = m_Geometry.TryGetAnglesForPosition(intersectionPoint, _name);
if (angle.IsNone)
{
Logger.LogWarning(Name, $"Cannot determine angle for position '{intersectionPoint}' corresponding to pixel '{pixel}'.");
}
else
{
result.Add(angle.IfNone(PointF.Empty));
}
}

There are two kinds of ugliness: - I have to use the IfNone(PointF.Empty) clause even when angle is guaranteed to be Some there. - I do not know how to get rid of the foreach in this situation. How can the code become clean?

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!

[Richard Deeming]

If you didn't want to log the failures, it could be as simple as:

m_Geometry.TryGetAnglesForPosition(intersectionPoint, _name).IfSome(result.Add);

Otherwise, something like this should work:

m_Geometry.TryGetAnglesForPosition(intersectionPoint, _name).Match(
point => result.Add(point),
() => Logger.LogWarning(Name, $"Cannot determine angle for position '{intersectionPoint}' corresponding to pixel '{pixel}'."));

There's also the C# 8 property patterns:

if (m_Geometry.TryGetAnglesForPosition(intersectionPoint, _name) is { IsSome: true } angle)
{
angle.IfSome(result.Add);
}
else
{
Logger.LogWarning(Name, $"Cannot determine angle for position '{intersectionPoint}' corresponding to pixel '{pixel}'.");
}

Or you could define a deconstructor as an extension method:

public static class OptionTExtensions
{
public static void Deconstruct<T>(this Option<T> option, bool isSome, T value)
{
isSome = option.IsSome;
value = isSome ? (T)option : default;
}
}
...
var (isSome, point) = m_Geometry.TryGetAnglesForPosition(intersectionPoint, _name);
if (isSome)
{
result.Add(point);
}
else
{
Logger.LogWarning(Name, $"Cannot determine angle for position '{intersectionPoint}' corresponding to pixel '{pixel}'.");
}

---

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[Bernhard Hiller]

Thanks, that was the major step for this issue. Afterwards, I could figure out the var tmp = intersections.Map(_intersection => m_Geometry.TryGet...ToList() monstrosity abolishing the foreach(... intersections). Functional programming feels odd when trying it for the first time.

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!