ASP.NET Core Bound<T> Concept

Bound.cs

/*
I wish ASP.NET Core had the concept of a `Bound` class. The Bound
class would be accessible to developers and be hydrated by the model binder to not only give
you the value the caller sent, but allow you to understand if the user expressed the intent
to give you that information.

There are multiple reasons why a value may not have been bound:

1. Failed Deserialization

{ "number" : "this is not a number" }

2. User Never Sent It

{ "number" : null }

3. The Consumer of the API (Another Developer) Forgot to Send it.

{}
*/
public class Bound<T> {

  /* properties */
  public bool IsAvailable  => Result == BindingResults.Available;
  public bool IsBindingFailed  => Result == BindingResults.BindingFailed;
  public bool IsUnavailable  => Result == BindingResults.Unavailable;
  
  // Unavailable, BindingFailed, Available, etc.
  public BindingResults Result {get;}
  public T Value {get;}
  public string OriginalValue {get;}    
}

public class ContactUsRequest {  
  // added in version 1
  public Bound<string> FullName {get;set;}
  // added in version 2
  public Bound<string> FirstName {get;set;}
  public Bound<string> LastName {get;set;}
}

/* How Would You Use It? */
/* 1. In an Action */
public IActionResult Post(ContactUsRequest request) 
{
  if (request.FullName.IsAvailable) 
  {
    // old version, let's split it
    var parts = request.FullName.Split(' ');
    request.FirstName = parts.FirstOrDefault();
    request.LastName = parts.LastOrDefault();
  }
  
  /* continue on */
}

/* 2. In an ActionAttribute */
- If the action argument looks a certain way, change it before it gets to the action

/* 3. At the Routing Level */
- Reroute to a completely different action based on binding outcome