That's very clear thank you. Some follow up questions:
In my case, I still need to notify every player that the resource is not
available anymore and that is a side effect.
Should I just make it idempotent so it doesn't matter if it's called more
than once.
If I check for the resource within the function passed to swap! and do my
side effect only when it's available, It should not happen more than once,
right ?
On Mon, Feb 1, 2016 at 3:27 PM, William la Forge <laforg...@gmail.com>
wrote:
> The easy way is the big atom approach. Put the entire structure in an atom
> and use swap! to make updates.
>
> First, the function passed to swap! should be free of side-effects, as
> swap! may need to call it more than once in the case of a collision.
>
> Second, within the function passed to swap! is where you check to see if
> the resource is available. If it is, you take it. Otherwise not.
>
> Now as for suitability. Note that the function passed to swap! must return
> the replacement value of your immutable structure. So it important
> that your structure records who got the resource being requested. And it
> looks like your structure handles that.
>
> No need to use compare and set. The swap! function is good enough. It is
> really a convenience function layered over compare-and-set.
> Sometimes swap! is not powerful enough, which is when you use
> compare-and-set.
>
>
> On Monday, February 1, 2016 at 7:29:39 AM UTC-5, Jeremy Vuillermet wrote:
>>
>> Hello,
>>
>> I'm making a game where players can choose a box in a grid to discover
>> what's behind it.
>>
>> My data structure is an atom with {:grid-size 5, :picks {5 "player1}}
>> where 5 is the box position in the grid.
>>
>> How can I be sure that two players can't pick the same box. From my
>> understanding, checking the box and then swaping if the box is free is not
>> enough.
>> So I guessed I should use compare and set but I only understand how it
>> works with simple atom like (atom 1).
>>
>> 2 questions then : Is my data structure adapted for that ?
>>
>> How to compare and set only for a nested path like [:picks 5] ?
>>
>> Thanks
>>
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