Switch coins.Amount to uint, consider using a deterministic map instead of a list

[cwgoes]

Ref https://github.com/cosmos/cosmos-sdk/pull/1218/files#r195270328

[cwgoes]

Depends on #553.

[ebuchman]

Unclear how we want to move forward with this.

My impressions are:

• we need to do something about it
• so long as we have a small number of coins, what we have is fine
• we don't even have a way to add new coins yet, and we're launching with just one, so we're fine for a bit
• if governance rolls out a new coin via hard-fork upgrade, this is still fine, until we have a lot of them
• by then we're hard-forking around anyways

In conclusion, I think we can punt on actually dealing with this for now.

Anyone disagree ?

[ValarDragon]

I agree that we can move deterministic map to post launch (especially since that will involve us creating our own datastructure), but I think coins.Amount should be made into a Uint prelaunch.

[jackzampolin]

Is this still an issue? I'm guessing yes.

[alexanderbez]

Definitely think this should be tackled pre-launch. Any opposition to this?

I like @ValarDragon's idea of using arithmetic coins (signed ints which users never really interact with) and "safe" or "regular" coins (unsigned ints that users do interact with and that is kept in state).

/cc @ebuchman @cwgoes

[ValarDragon]

Oh sorry I forgot to write up the various things into this issue! To recap the arithmetic coins idea,

I think the result of any arithmetic should be of type "arithmetic coins". Arithmetic coins can have negative denoms, so you can easily have things like A - B + C, where its negative after (A - B) but positive at the end. You then have to cast arithmetic coins into a normal coins, i.e. arithmetic_coins.Safe_Coins (better name pending)

Whenever you parse a coin value, or write a coin value, it would be the regular coins. So state would only have these regular coins, and fees would also only be read as regular coins.

I like this because it enables fast addition laws, while also giving us the safety we'd want.

I also think the coin denominations should be sorted, not a deterministic map. The reason I am in favor of this is because it makes the addition law much quicker.

[cwgoes]

I think the result of any arithmetic should be of type "arithmetic coins".

I agree in general but I'm not sure this is worth the complexity right now, given that we don't actually perform A - B + C anywhere in the codebase (that I can find).

I also think the coin denominations should be sorted, not a deterministic map.

This is now true. Maybe this is good enough, although I still don't like that we're storing all the denomination strings repeatedly in state.

[ValarDragon]

This is now true. Maybe this is good enough, although I still don't like that we're storing all the denomination strings repeatedly in state.

Agreed, I was actually writing another issue for exactly that last night, and just didn't get a chance to finish it then lol.

[cwgoes]

This has been done.