Do not depend on Coord's instance methods from serialized board state…

[mateusazis]

… in checkers.

Fixes #750.

Checklist

• Use a separate branch in your local repo (not master).
• I've read and agree with the contribution guidelines.

[vdfdev]

Thank you!

[leocaseiro]

Thank you @mateusazis and @flamecoals!

[vdfdev]

@mateusazis Can we get rid of this class entirely? This is a known issue that classes are not serializable, so I am worried another corner case might bring the same issue as we are calling other methods on the game logic. I missed this during review, sorry.

[mateusazis]

We can. But, as you said, this doesn't prevent this bug from coming back. The boardgame.io docs warn about it but also don't prevent it. Some ideas that came to my mind were:

• At compile time: annotate the top-level state interface with a decorator and make sure the class no methods (not sure if this is doable in Typescript).
• At test time: between turns, serialize and de-serialize the game state when running in Local mode. This would have made our unit tests catch the bug.

Ideally, the 2nd approach would go into the boardgame.io lib.

[vdfdev]

@mateusazis I am not sure if the first approach is feasible either.

Let's go with the second approach, I think this would also help other developers on the boardgame.io community. We can probably allow for a "strict check" during testing on the boardgame.io Client API. I created #754 to keep track of the work.

[vdfdev]

For now, I sent you @mateusazis #755 to remove the class from checkers entirely.