consider using Immer

People get immutability wrong all the time (self included). Even the ones that know what they’re doing often have to write some really messy code when deep state updates are involved.

Immer seems to achieve the best of both worlds. We should consider bundling it in (and possible have a flag that allows turning it off for people that prefer not to use it).

move: (G, ctx) {
  G.hand++;
  G.deck--;
}

vs.

move: (G, ctx) {
  return {
    ...G,
    hand: G.hand + 1,
    deck: G.deck - 1,
  };
}

Open questions:

1. How do we indicate invalid moves ( #292 ) in this approach?

[nicolodavis]

Supported in 0.28.0.

[philihp]

I can see the advantage of having current code errantly mutating state being safe once this is implemented. Immer automatically binds this to the draft of G inside of produce, so I would expect both should work.