VIP: Structs as arguments

[fubuloubu]

Simple Summary

Accept Structs are args.
Depends on #300

Abstract

It would be way easier to operate with different datatypes if we had better ways of interacting with more complex types like structs.

Motivation

Solidity allows accepting structs as arguments via their experimental ABIEncoderV2 pragma.
I believe v0.5 will allow this without an experimental pragma, and it will come out soon.
We should adopt this standard to make it easier to work with structs in different ways.

Specification

# MyStruct is a struct type as defined in #300
def accepts_struct(a: MyStruct):
    ...

(Optional) allow structs to be returned as outputs.

def returns_struct() -> MyStruct:
    ...

Backwards Compatibility

No modifications of existing syntax
ABI Encoder will need to be modified, but should be backwards compatible

Copyright

Copyright and related rights waived via CC0

[jacqueswww]

Approved, dependency on #300.

[charles-cooper]

Remaining stuff after #1115 is merged

• Pass in structs to public functions (requires eth-abi updates to test)
• Return nested structs from functions (requires eth-abi updates to test)
• Pass nested structs as args
• Pass/return structs with dynamic data

[jacqueswww]

Meeting Note: When eth-tester relase gets cut, we can look at implementing the final steps listed by Charles.

[fubuloubu]

We should be able to finish the work suggested as remaining in this PR at this point.

[fubuloubu]

As per this comment, @charles-cooper says there are a few things left to do to complete this VIP. I think we could punt on the last three of his suggestions to another issue, and I'd also like to note that passing structs to public functions works in master

Motion to close?

[charles-cooper]

yeah we could punt to another issue

[fubuloubu]

Closing as the majority of this functionality was implemented in #1115

Note that some corner cases exist, whose progress is now being tracked in #955/#1200 (same resolution), #1170, and #1648