snip-2.md

snip	title	author	status	type	category	created
2	Token Standard	Abdelhamid Bakhta <[email protected]>	Draft	Standards Track	SRC	2022-06-03

Simple Summary

A standard interface for tokens.

Inspired by EIP-20.

Abstract

The following standard allows for the implementation of a standard API for tokens within smart contracts. This standard provides basic functionality to transfer tokens, as well as allow tokens to be approved so they can be spent by another on-chain third party.

Motivation

A standard interface allows any tokens on StarkNet to be re-used by other applications: from wallets to decentralized exchanges.

Specification

Token

Methods

NOTES:

• The following specifications use syntax from Cairo 0.8.1 (or above)

name

Returns the name of the token - e.g. "MyToken".

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.

    func name() -> (name: felt):
    end

symbol

Returns the symbol of the token. E.g. "HIX".

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.

    func symbol() -> (symbol: felt):
    end

decimals

Returns the number of decimals the token uses - e.g. 8, means to divide the token amount by 100000000 to get its user representation.

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.

    func decimals() -> (decimals: felt):
    end

totalSupply

Returns the total token supply.

    func totalSupply() -> (totalSupply: Uint256):
    end

balanceOf

Returns the account balance of another account with address account.

    func balanceOf(account: felt) -> (balance: Uint256):
    end

transfer

Transfers amount amount of tokens to address recipient, and MUST fire the Transfer event. The function SHOULD throw if the message caller's account balance does not have enough tokens to spend.

Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.

    func transfer(recipient: felt, amount: Uint256) -> (success: felt):
    end

transferFrom

Transfers amount amount of tokens from address sender to address recipient, and MUST fire the Transfer event.

The transferFrom method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf. This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies. The function SHOULD throw unless the sender account has deliberately authorized the sender of the message via some mechanism.

Note Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.

    func transferFrom(
            sender: felt, 
            recipient: felt, 
            amount: Uint256
        ) -> (success: felt):
    end

approve

Allows spender to withdraw from your account multiple times, up to the amount amount. If this function is called again it overwrites the current allowance with amount.

    func approve(spender: felt, amount: Uint256) -> (success: felt):
    end

allowance

Returns the amount which spender is still allowed to withdraw from owner.

    func allowance(owner: felt, spender: felt) -> (remaining: Uint256):
    end

Events

Transfer

MUST trigger when tokens are transferred, including zero value transfers.

A token contract which creates new tokens SHOULD trigger a Transfer event with the from_ address set to 0x0 when tokens are created.

@event
func Transfer(from_: felt, to: felt, value: Uint256):
end

Approval

MUST trigger on any successful call to approve(address _spender, uint256 _value).

@event
func Approval(owner: felt, spender: felt, value: Uint256):
end

Implementation

Example implementations are available at

• OpenZeppelin implementation

History

Copyright

Copyright and related rights waived via MIT.