Converting between union and Maybe

[divanburger]

When converting from an union to a Maybe I have to write code like this:

Session :: struct {
	key: string,
	user_id: Maybe(int)
}

ResultValue :: union {
	int,
	string,
	bool
}

row: map[string]ResultValue
session: Session

user_id, ok := row["user_id"].(int)
session.user_id = ok ? user_id : nil

As it is not possible to convert directly from an union to a Maybe.

I though I could maybe write something like:

session.user_id = row["user_id"].(int) or_else nil

That unfortunately gives the error Cannot convert untyped value 'nil' to 'int' from 'untyped nil' as it is trying to convert the nil directly to the type of the value first without realising that the Maybe supports both. The ternary operator works correctly though.

My proposal is either making the or_else not try to convert to the type of the value and instead check the type that is supported by the context (the left-hand side of the assignment in this case), or maybe add syntax to convert from an union with a type assert to a Maybe. Maybe something like session.user_id = row["user_id"].?(int). I don't really like this syntax but maybe there is something similar that could work? session.user_id = row["user_id"].(Maybe(int)) wouldn't make sense as the union could have a Maybe(int) in it.

Thoughts?

[JesseRMeyer]

We discussed this in the discord and it looks like or_else should support this. Thanks for the report.