reserve 22 as ttHOOK_SET

[RichardAH]

We'd like to reserve 22 as SetHook transaction type. This tt will eventually allow configurable behaviour on accounts for send and receive events.

[nbougalis]

Seems reasonable. Just noting that the downside of reserving is that we've basically burned an ID and there's only 64k of them and I don't know that we need to reserve the transaction ID at this time, but it shouldn't really be a problem to do so.

Please consider rewording your commit:

Reserve transaction type identifier for event hooking:

Event hooks will allow accounts to introduce configurable behavior
in response to send and receive events.

P.S.: Let the English vs. U.S. spelling wars begin. "behaviour"... 🙄

[mDuo13]

I'm not concerned about burning one ID (number 153) out of 64,000. 😆

Hooks is an interesting idea. I think the scope will be paramount. Too big, and you end up with Solidity¹; too small, and you need to keep growing it with more features later. Sometimes having a bunch of specialized tools is useful, sometimes it's too complex and having one all-purpose tool is better.

¹ Solidity is cool, but bugs in smart contracts are a big problem (even the DAO couldn't get their right on the first try, and most of us don't have the option of hardforking the network if we screw up) and the more complexity, the more opportunity for bugs. Also, the more logic and state data you store on-ledger, the harder your scaling problems become.

[nbougalis]

👍

Should probably be squashed into one commit on merge, with a commit message:

Reserve transaction type and error codes for event hooking:

Event hooks will allow accounts to introduce configurable behavior
in response to send and receive events.

[carlhua]

I am giving a Passed label as this is trivial.