String Format object extension

Question

I wrote an extension to create a string-representation by an object:

public static string ToString<T>(this T @this, Func<T, string> predicate) where T: class
{
    return predicate(@this);
}

So I can do something like

return handler.GetUserById(id)?.ToString(x => $"{x.LastName}, {x.FirstName}");

which gives me either null if the user is null or otherwise e.g. "Miller, Peter"

My question: is this a good extension? Makes it sense? Anything I didn't consider? And what about the null-thing? Should I check the null value in the extension? Imho, the thrown NullReferenceException is okay, if s.o. calls this with a null object.

Answer 1

There are not much to review, so to answer your questions:

1. It's a good extension if you can see it useful in more than one place.
2. It makes sense.
3. I can't see anything else to consider - a null check on the predicate maybe?
4. If the exception thrown by the predicate when @this is null is good enough for you, don't bother further.

---

I don't see why the restriction where T: class is necessary

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If you always want to generate a string containing a list of properties (or another predefined format), you could change the signature to:

public static string ToString<T>(this T @this, params Func<T, object>[] getters)
{
  return string.Join(", ", getters.Select(g => g(@this)));
}

called as:

handler.GetUserById(id)?.ToString(p => p.LastName, p => p.FirstName)

so that you don't have to format the input when calling the extension.