---
eip: 2135
title: Consumable Interface
author: Zainan Victor Zhou (@xinbenlv)
discussions-to: https://github.com/ethereum/EIPs/issues/2135
status: Draft
type: Standards Track
category: ERC
created: 2019-06-23
---

## Simple Summary
An interface marking certain digital assets being consumable. 

## Abstract
The interface identifies functions and events needed for creating a contract to be able to mark a digital asset as "consumable", and react to the request of "consumption".

## Motivation
Being a digital assets sometimes means a consumable power. One most common seen examples would be a concert ticket. It will be "consumed" at the moment the ticket-holder uses the ticket to get access to enter a concert. 

By having a standard ERC interface, the Ethereum ecosystem can interoperate to provide services, clients, UI, and inter-contract functionalities on top of this very general use-case.

## Specification
The standard will mainly contain the following interface.

### The required interface

```solidity
pragma solidity ^0.5.8;

contract EIP2135 {
  // The main consume function
  function consume(uint256 assetId) public returns(bool success);

  // The interface to check whether an asset is consumable.
  function isConsumable(uint256 assetId) public view returns (bool consumable);

  // The interface to check whether an asset is consumable.
  event OnConsumption(uint256 indexed assetId);
}
```

## Rationale

The function `consume` performs the consume action. Being an interface standard, 
this EIP does not impose any assumption of

 - who has the power to perform such activity. 
 - under what condition such consumption can occur.
 
It does, however, assume the asset can be identified in a `uint256` assetId as in th parameter. A design convention and compatibility consideration is put in place to follow the ERC-721

The event notifies subscribers whoever are interested to learn an asset is being consumed. The boolean function of `isConsumable` can be used to check whether an asset is still consumable. 

To keep it simple, this standard *intentionally* contains no functions or events related to creation of a consumable asset. This is because the creation of a consumable asset will need to make assumption of the nature of an actual use-case. If we see some common use-case of creation, we can have another follow up standard.

We also left out metadata associated to the consumables from the standard. If necessary, related metadata can be created with a separate metadata extension interface like [`ERC721Metadata`](https://eips.ethereum.org/EIPS/eip-721)

## Backwards Compatibility

This interface is designed to be compatible with ERC-721.

## Implementation

A reference implementation accompany with tests of **ERC-721 based ticket** contract is built and you can found it [here](https://github.com/xinbenlv/eip-2135/blob/master/impl/contracts/Ticket721.sol).

See [Github/xinbenlv/eip-2135/impl](https://github.com/xinbenlv/eip-2135/tree/master/impl)

## Test Cases

See [Github/xinbenlv/eip-2135/impl/test](https://github.com/xinbenlv/eip-2135/tree/master/impl/test)

## Reference

### Standards
- [ERC-721](https://eips.ethereum.org/EIPS/eip-721)

## Copyright
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).