VIP: Change bytes length notation

[jacqueswww]

Preamble

VIP: 714
Title: Change bytes length notation
Author: Jacques Wagener
Type: Standard Track
Status: Draft
Created: 2018-03-22

Simple Summary

Change the bytes decleration syntax to resemble a lists' syntax.

Abstract

Change the byte length syntax on declaring a bytearray.

Motivation

The motivation is critical for VIPs that add or change Vyper's functionality. It should clearly explain why the existing Vyper functionality is inadequate to address the problem that the VIP solves as well as how the VIP is in line with Vyper's goals and design philosopy.

Specification

Currently bytearray size are set using the the smaller-than-or-equal operator <=. This VIP will replace it to use the square bracket to indicated the byte size.
From

abytearray: bytes <= 3

To

a: bytes[3]

This makes it slightly more readable and standardised - because list lengths use the same square bracket subscript notation e.g.

alist: int128[7]

Backwards Compatibility

Not backwards compatible. Fully override the old style.

Copyright

Copyright and related rights waived via CC0

[fubuloubu]

I'm on board!

[fubuloubu]

One thing to consider: mappings

a: bytes[4][address] and b: int128[bytes[3]]

Does that look okay? I think it does

[jacqueswww]

@fubuloubu I think it does. But I want this VIP and #564 and to happen before we go beta.

From my side it's the last 2 big changes before, I am happy with the syntax to go beta.