CODEWITHSUNDEEP
kdb+
cjm2671
cjm2671

Reputation: 19486

Are side-effects sometimes necessary when using KDB?

Let's say I have a state variable s.

I've got a .z.ws hook that responds to websocket messages and runs:

.z.ws: {handleMsg x}

Do I have to declare s as global for handleMsg to be able to update s?

Ideally, what I'd want is something like:

s: handleMsg[s;x]

where handleMsg is a pure function (it doesn't affect any globals on the inside).

Should I declare s as global and then try to do this assignment inside the websocket callback?

Upvotes: 0

Views: 95

Answers (1)

terrylynch
terrylynch

Reputation: 13657

You don't pre-declare variables as global in kdb, they're global if you make them global at any point (and if you reference them as a global).

q)func:{x+1}

/s is local and treated as such
q){s:func[1]}[]
2

/it is not a global
q)s
's

/this would make it global
q){`s set func[1]}[]
`s
/or
q){s::func[1]}[]

/now it's global
q)s
2

/but a local of the same name would take preference
q){s:func[100];s}[]
101
q)s
2

/you can force-reference the global if required
q){s:func[100];value `s}[]
2

So you're in complete control over what's global, what isn't, when you're referencing a local and when you're referencing a global.

Upvotes: 3

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