What is the current NUnit's ApplyTo(object) implementation

I want to make a new

Constraint

but surprised that I could not follow this official guidelines, because the abstract ApplyTo given by Unity's NUnit takes an object and has no type params. I want to use

TActual

in my

ApplyTo

implementation.

Code (CSharp):

1.         public virtual ConstraintResult ApplyTo<TActual>(ref TActual actual);
2.         public virtual ConstraintResult ApplyTo<TActual>(ActualValueDelegate<TActual> del);
3.         public abstract ConstraintResult ApplyTo(object actual);

In the official NUnit and even from this repo https://github.com/Unity-Technologies/nunitv3 it is stated that there is no such overload, but the abstract signature already has

TActual

and is linked directly from

Assert.That<TActual>(TActual ___  , ...)

Code (CSharp):

1.         public abstract ConstraintResult ApplyTo<TActual>(TActual actual);
2.         public virtual ConstraintResult ApplyTo<TActual>(ActualValueDelegate<TActual> del)
3.         public virtual ConstraintResult ApplyTo<TActual>(ref TActual actual)

So, in the official NUnit code,

Assert.That<TActual>(TActual ___  , ...)

will go to the abstract one complete with

TActual

type params. What about Unity's? The following 3 generic overloads of

That

is available, I would like to know how could I get

TActual

into my custom

Constraint

. Are these information lost and became just

object

?

Code (CSharp):

1. public static void That<TActual>(TActual actual, IResolveConstraint expression);
2. public static void That<TActual>(TActual actual, IResolveConstraint expression, string message, params object[] args);
3. public static void That<TActual>(TActual actual, IResolveConstraint expression, Func<string> getExceptionMessage);

At least I want to know how

public virtual ConstraintResult ApplyTo<TActual>(ref TActual actual);

could be called from

Assert.That

so I could use the type and just ignore the

ref

. As for

ActualValueDelegate

ones, I don't really want to write

Assert.That( () => myValue)

every time in order to trigger it. Or better, I want to see the source code of NUnit that is included with 2019.1. Thank you.