I have some generic method
T SomeMethod(Func<T> func){
T result = func();
if (result != null)
{ //.....}
}
It works good if T is class. But what should I do if T is struct? How can I check if result == default(T) in case if T is struct?
P.S. I don't want to use the constraint where T: class or Nullable types.
If T is compiled to be a struct then the comparison with null will always evaluate to false. This is covered in section 7.9.6 of the C# language spec
If an operand of a type parameter type T is compared to null, and the runtime type of T is a value type, the result of the comparison is false.
null it still returns null.
Nullable<T> (which is a struct itself), as is the ability to assign null. That's baked into the language (and perhaps the runtime; I'm not certain about that) and isn't something that can be duplicated on user types.
if (result != null || result==false) ? Does it work for structs?A more idiomatic way of doing this would be to follow the lead of things like int.TryParse.
public delegate bool TryFunction<T>(out T result);
T SomeMethod(TryFunction<T> func)
{
T value;
if(func(out value))
{
}
}
int.TryParse's lead, but instead builds on it. I don't think this is idiomatic, but it isn't a bad idea. Whether it generically solves the original problem or just side-steps it is a different question (one I can't answer - check my comment on the OP, since I think the question can't be answered generically).
Func<out T, bool> won't compile. You would have to create new delegate type for that.out parameter and return a bool indicating success. I'm calling it idiomatic because this technique is used in several places in the framework, and seems to fit the bill.Consider using default(T):
private T SomeMethod<T>(Func<T> func)
{
var result = func();
if (result.Equals(default(T)))
{
// handling ...
return default(T);
}
return result;
}
T is a reference type, this will throw a NullReferenceException.
null? What if a reference type has just been constructed - is that equivalent? I think this can't be answered generically, but must be answered on a case-by-case basis depending on your scenario.default(T) where T : class == nullif(result != null).