Vyper: VIP: Modify event declaration syntax to resemble that of struct

[iamdefinitelyahuman]

Simple Summary

Change this:

Transfer: event({_from: indexed(address), _to: indexed(address), _value: uint256})

to this:

event Transfer:
    _from: indexed(address)
    _to: indexed(address)
    _value: uint256

Motivation

The current approach to declaring an event reads as though there is a variable being created, with it's type defined from the result of a call to an event function. This is misleading because:

1. The created event is not a variable. You cannot assign to it during declaration, or reference it except as a callable member of log.
2. event, though appearing to be a function, is not a function. And type annotations are not typically declared as the result of a function call.
3. The reliance on the ordering of dictionary keys inside event is not a standard python behavior until version 3.7. Declaring the fields in this way does not intuitively read as though they are sequenced.

By instead using the struct-style declaration, we make it more clear that this not a simple variable, and that the members inside are sequenced.

Backwards Compatibility

This will be a rather large breaking change, we should definitely discuss it at length. If it is approved, it probably belongs in the 1.0rc release.

Copyright

Copyright and related rights waived via CC0

[fubuloubu]

Should changing the way logs are emitted also be a part of this proposal?

(From log.<EventName>({...}) to log(EventName({...})))

Example:

event MyEvent:
    arg1: indexed(address)
    arg2: uint256
...
log(MyEvent({msg.sender, msg.value}))
...
# Extended lines...
log(MyEvent({
    msg.sender,
    msg.value,
}))

[jacqueswww]

Approved; makes to align the syntax with struct.

[fubuloubu]

@iamdefinitelyahuman Let's make this happen with 0.2.0?

[iamdefinitelyahuman]

For an event without any arguments:

event Foo: pass

[iamdefinitelyahuman]

for emitting events, i think log is better as a statement. Also, I don't like the use of curly brackets inside the call, I don't think they serve any purpose.

To me the ideal syntax would be:

log MyEvent(msg.sender, msg.value)

[fubuloubu]

:ship: :ship: :ship: