Hello again =)!
I'm doing advent of code to improve my Nim and encountered a problem today
trying to create a string type with specific constraints. I'd like to
understand type constraints if they exist, not just for this problem but
generally.
Today's problem deals with hands of poker represented as 5 character strings
containing any of the following cards/chars {'A', 'K', 'Q', 'J', 'T', '9', ...,
'2'}. So a valid hand would look like 'AKT33' for example, while non valid hand
would look like 'AKT333' (6 chars) or 'ABCDE' (wrong character set).
I tried with concepts:
type
HandLike = concept x
x is string
len(x) == 5
HashSet(x) == {"A", "K", "Q", "T", "9", "8", "7", "6", "5", "4", "3",
"2"}
Run
But after reading [this
question](https://stackoverflow.com/questions/71242378/nim-how-to-constrain-an-existing-type),
in which they have a very similar problem (DNA strings), it seems that's not
what concepts are for.
My second idea is to do something like:
type
Card = enum
CA, CK, CQ, CJ, CT, C9, C8, C7, C6, C5, C4, C3, C2, C1
Hand = object
card1, card2, card3, card4, card5: Card
Run
But it's going to require a lot of boilerplate to convert, compared to just
applying constraints on a string type. Also in an hypothetical where I have
more than 5 cards, for example to represent a 52 cards deck, it starts to
become unwieldy.
Their answer to the DNA problem was just to parse it with a distinct string but
I'd like to encode the constraints directly into the type, is it possible?
