Any plans on making get public?

[iK4tsu]

Although SumType is meant to be a @safe algebraic type, sometimes we might want to extract the value from it directly. If the user knows what value is contained within SumType, then always resorting to match, its heavy usage might become a little tedious to write. I propose making get, or other function, public so that this can be avoided. Such function needs to be @system as it can lead to undefined behavior.

[pbackus]

No, get will never be public.

If you want something similar, I suggest a tryGet function like the following:

T tryGet(T, ST)(ST st)
    if (isSumType!ST)
{
    return st.tryMatch!((T value) => value);
}

This will throw an exception when the requested type is not found.

[iK4tsu]

Yes, however that doesn't work with betterC. If not get, then maybe a @system version of it. But if it isn't in your plans, which is understandable, then I'll just keep using match.

That being said, I don't think a function to extract the value directly would damage the lib in any way, if it were @system and well documented. It would come down to the user's choice if he wanted to use the function or not.

[pbackus]

Good API design is as much about what you leave out as about what you include. I want sumtype to guide users into the pit of success, and providing a function that crashes at runtime if you use it incorrectly is contrary to that goal.

[iK4tsu]

How about adding a version of tryMatch/tryGet suitable for betterC. This would assert if the requested type wasn't found.

[pbackus]

You can write it yourself if you really want it. I will not include such a function in the sumtype library, for the reason stated above.

[FFY00]

Hold my beer while I fork the standard library for my project... because I want to use something in betterC...?

[iK4tsu]

I don't know if this covers all cases, but based on your example above:

T tryGet(T, ST)(ST st)
	if (isSumType!ST)
{
  	static if (st.Types.length == 1)
      	return st.match!((T value) => value);
  	else
      	return st.match!(
        	(T value) => value,
        	function T (_) { assert(false); }
    	);
}

Not really what I want, but it might do as a workaround.

[pbackus]

Personally I would recommend something like this for BetterC (and in general, honestly):

Nullable!T get(T, ST)(ST st)
    if (isSumType!ST)
{
    return st.match!(
        (value) {
            static if (is(typeof(value) == T))
                return nullable(value);
            else
                return Nullable!T();
        }
    );
}