What is the behavior of SET_DELEGATE in particular cases

Question

The Michelson Documentation does not say much about this function:

SET_DELEGATE: Forge a delegation.
:: option key_hash : 'S   ->   operation : 'S

This left me wondering about its behavior and if can produce an error in any certain cases.

1. I am assuming SET_DELEGATE on NONE removes the delegationn and SOME key_hash sets the key_hash as the delegate, is this correct?

2. Will it produce an error if the key_hash is not a baker or if it was once a baker and no longer is?

3. Will it produce an error if the baker at the key_hash is fully delegated to?

4. Are there any other conditions in which SET_DELEGATE can produce an error?

Answer 1

1. That's correct - this constructs an operation, much the same as when you use client to set delegate for ... or withdraw delegate from ....

2. If the key_hash is not a baker, it will produce "Unregistered delegate" error (unless it's self-delegation to register a new baker or to activate a inactive baker). It is currently not possible to de-register a baker.

3. If it's already delegated to the same baker, it will lead to "Unchanged delegated" error.

4. • Trying to de-register baker with SET_DELEGATE NONE leads to "Forbidden delegate deletion"
   • Trying to change delegate of a register baker also leads to "Forbidden delegate deletion"
   • Trying to re-activate an already active baker leads to "Delegate already active"
   • Trying to register a baker on account with 0 balance leads to "Empty delegate account"