SWIFT-355 Make option properties mutable

[ncarbon]

Makes all option properties mutable. Option properties are declared with 'var' instead of 'let'.

[kmahar]

very nice! 🙂 just a couple of comments. please let me know if you have any questions about them!

[kmahar]

so I just realized there is something a little tricky that we need to handle in FindOptions.

we allow the user to provide a CursorType input to the initializer. CursorType is an enum with three possible values: nonTailable, tailable, and awaitData.

however, when we send that info to libmongoc in the MongoCollection.find method, we need to send it as two bools instead: tailable and await. currently, we decide the values of tailable and await in the FindOptions initializer here based on whatever CursorType the user specifies.
and then, we include tailable and await in our CodingKeys list, which lets us specify which values in FindOptions actually get sent to libmongoc.

currently, this works fine because we never change cursorType outside of the initializer.

however, now a user could do something like the following:

var options = FindOptions(cursorType: .tailable) // the initializer will set tailable=true, await=false
options.cursorType = .tailableAwait // now we should have tailable=true, await=true, but we didn't update their values!

basically, we need a way to keep tailable and await in sync with cursorType.

I think the simplest way to fix this would be to make FindOptions.cursorType a computed property. you can read a little bit more about them on this page (scroll down to "Computed Properties" section.) take a read through that and then let's talk more in person later today about how we can use it here 🙂

[patrickfreed]

I think we can also leave tailable and await as let since we don't want to be modifying them directly but only through the new cursor type property.

edit: disregard this

[kmahar]

If we declare them with let, how would we modify them as needed in my example above?

[patrickfreed]

[nit] this comment can be removed.

[patrickfreed]

I think we can also leave tailable and await as let since we don't want to be modifying them directly but only through the new cursor type property.

edit: disregard this

[kmahar]

suggestion for a couple more test cases to add. otherwise looks great!

[kmahar]

awesome job, LGTM 👏

[patrickfreed]

lgtm! great work on your first ticket