# SIP 43: Address Resolver Source

Author Justin J Moses Implemented 2020-02-28

## Simple Summary

Add a new AddressResolver contract for smart contract lookups.

## Abstract

Add an AddressResolver contract stores the addresses of all interoperable smart contracs within the Synthetix protocol, and provide access to this resolver in all smart contracts that need to communicate with the others.

## Motivation

The Synthetix protocol is supported by a fairly complicated network of smart contracts. However, due to the limits put on smart contracts sizes by the EVM (see EIP-170) only so much logic and state can fit into a single contract. Moreover, to reduce the need to upgrade key contracts and to provide better adherence to the single-responsiblity-principle, having more smaller, single-purpose contracts is preferable.

In order to facilitate this intercontract communication, a contract respository (based on the Service Locator pattern) is the most robust and bytecode efficient solution.

## Specification

The AddressResolver needs a mechanism with which to import mulitple addresses, and this needs to be restricted to the owner. This import should be mutative, such that any subsequent imports of the same name will simply overwrite previous versions.

It will be the responsibility of the deployment (and eventually migration contracts) to ensure that new addresses are imported after they are deployed.

The keys of this repository will be bytes32 encoding of the existing contract names, which are all described in our list of addresses in the documentation.

Every contract that wishes to use the AddressResolver will need to inherit from MixinResolver (by leveraging multiple inhertance, we an think of this functionality as being a mixed into the target contract).

## Rationale

We analyzed how others have approached this task - in particular Colony’s implementation of an address lookup system. Ours is somewhat different in that it simply needs to store contract names and allow simple lookup. Seeing as we already have a system in place to uniquely identify contracts by a string name - converting these to bytes32 seems the most straightforward and gas efficient.

## Test Cases

See https://github.com/Synthetixio/synthetix/pulls/383

## Implementation

See https://github.com/Synthetixio/synthetix/pulls/383

Copyright and related rights waived via CC0.