VIP: Use uint256 for public array getters

[iamdefinitelyahuman]

Simple Summary

When an array is declared public, the generated getter should accept uint256 instead of int128 in order to handle the lookups.

Motivation

We do not allow array lookups with negative numbers, so the use of int128 is unintuitive.

Specification

As an example, the following variable:

foo: public(address[3])

Should produce a getter with the following signature:

def foo(arg0: uint256) -> address: constant

Backwards Compatibility

This is not a breaking change, but it does amount to a deviation in expected behavior.

Dependencies

Not dependent, but related to #1979

Copyright

Copyright and related rights waived via CC0

[fubuloubu]

It actually is a breaking change, because it changes the Method ID of the getter function. I think this is a good thing though, as it will match the Solidity implementation.

[iamdefinitelyahuman]

Ahh, I forgot about interfaces we generate from other contracts. Was thinking it wasn't breaking since it would only affect newly compiled contracts. Good call.