Question

I can’t believe I can’t google this. I don’t know what to google.

public static T GetValue<T>(T defaultValue)
{
  if (T is bool) // <-- what is the correct syntax here?
    return (T)true; // <-- I don't think this works either
}

EDIT: Sorry I didn’t mention, the function above is only to show my question. It’s not a real function. Thanks everyone for the answers!

Answer 1

If one must use this same method/signature and must use the type of T (and there are reason for such, although if there are not then see Albin’s answer):

public static T GetValue<T>(T defaultValue)
{
  // Need to use typeof to get a Type object for bool, just as with T
  if (typeof(T) == typeof(bool)) {
    // Need to say "get out of my way C#"
    // The first cast to object is required as true (bool) is
    // otherwise not castable to an unrestricted T.
    // This widen-restrict approach could result in a cast error,
    // but from the above check it is known that T is bool.
    return (T)(object)true;
  }
  // .. other stuff that .. does stuff.
}

However, explicitly returning true (which is not the default value for a boolean) and ignoring defaultValue entirely otherwise seems .. suspect. But – It compiles! Ship it!

Notes:

• The use == for Types will not work reliably for subclasses (but it’s okay because bool is a structure so subtypes are not an issue). In those cases, look at IsAssignableFrom.
• typeof(T) is not necessarily the type of the value passed in (which could be null for reference types). This, along with subtypes, can lead to subtle variations to approaches that use is on the value.