How to call a method with a generic constraint using a type parameter without the constraint?

Question

Let's say I have a method:

public void ExampleMethod<T>(T x) where T : struct // or new()
{
    // example usage, similar to what's actually happening
    var z = (T)Enum.Parse(typeof(T), privateFieldOfTypeString);

    // do something depending on values of x and z
    // possibly using other methods that require them being enums

    // or in case of the new() constraint:
    // var t = new T() and do something together with x
}

and I want to use it as follows:

public void CallerMethod<S>(S y)
{
    if (typeof(S).IsEnum) // or some other invariant meaning that `S` is "new()able"
    {
        ExampleMethod(y); // won't compile
    }
}

So, during run-time I know that S satisfies the constraint for ExampleMethod<T>. I know it's possible to call it using reflection, something along the lines of:

this
    .GetType()
    .GetMethod(nameof(ExampleMethod<object>))
    .MakeGenericMethod(typeof(S))
    .Invoke(this, new object[] { y });

Is it possible without reflection?

Note: this is a simplified code from a real-life example and obviously I have no control over the signatures of these methods, hence the answers "add the constraint to CallerMethod" and "remove the constraint from ExampleMethod" are invalid.

Yes, the whole thing should be redesigned so the whole problem wouldn't appear at all. But as often in real-life "the whole thing" is too big, too coupled and too risky to rewrite. Some requirements have changed in an unexpected way - hence the apparent code smell, which I'm trying to minimize by hiding it in a single nasty-looking place.

Answer 1

You could use dynamic:

if (typeof(S).IsEnum)
{
    ExampleMethod((dynamic)y);
}

Answer 2

If the enum types are known, one possibility, though verbose, would be to convert to known types.

For example, as a starting point,

public void CallerMethod<S>(S y) {
    if (typeof(S).IsEnum) {
        if (y is KnownEnum) {
            var z = (KnownEnum)Enum.Parse(typeof(S), y.ToString());
            ExampleMethod(z);
        }
        if (y is KnownEnum2) {
            var z = (KnownEnum2)Enum.Parse(typeof(S), y.ToString());
            ExampleMethod(z);
        }
        //...
    }
}

Answer 3

In your specific case you can just cast to an int.

public void CallerMethod<S>(S y)
{
    if (typeof(S).IsEnum)
    {
        ExampleMethod((int)y);
    }
}

Answer 4

You could utilise operator overloading; define multiple explicit versions of CallerMethod that can all successfully make a follow on call to ExampleMethod

CallerMethod(Enum1 value) { ExampleMethod(value); }
CallerMethod(Enum2 value) { ExampleMethod(value); }
CallerMethod(Enum3 value) { ExampleMethod(value); }

etc.

If there are a large number of growing types that need a version of CallerMethod you could write a T4 template to generate a partial class with all implementations.