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Token Standard

CIP-20 ● Category: CBC ● Tag: FINAL ● ● 4 min de lectura

A standard interface for tokens.

Abstract​

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

Motivation​

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

Specification​

Token​

Methods​

NOTES:

  • The following specifications use syntax from Ylem 0.8.4 (or above).
  • Callers MUST handle false from returns (bool success). They MUST NOT assume that false is never returned!
name​

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

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

function name() public view returns (string)
symbol​

Returns the symbol of the token, e.g., "CTN".

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

function symbol() public view returns (string)
decimals​

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

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

function decimals() public view returns (uint8)
totalSupply​

Returns the total token supply.

function totalSupply() public view returns (uint256)
balanceOf​

Returns the account balance of another account with address _owner.

function balanceOf(address _owner) public view returns (uint256 balance)
transfer​

Transfers _value amount of tokens to address _to and MUST fire the Transfer event. The function SHOULD throw if the 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.

function transfer(address _to, uint256 _value) public returns (bool success)
transferFrom​

Transfers _value amount of tokens from address _from to address _to, 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, for example, allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies. The function SHOULD throw unless the _from 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.

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
approve​

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

NOTE: To prevent attack vectors like the one described here, clients SHOULD ensure they create user interfaces that set the allowance first to 0 before setting it to another value for the same spender. However, the contract itself shouldn't enforce this to maintain backward compatibility with contracts deployed earlier.

function approve(address _spender, uint256 _value) public returns (bool success)
allowance​

Returns the amount which _spender is still allowed to withdraw from _owner.

function allowance(address _owner, address _spender) public view returns (uint256 remaining)

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 Transfer(address indexed _from, address indexed _to, uint256 _value)
Approval​

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

event Approval(address indexed _owner, address indexed _spender, uint256 _value)

Implementation​

There are already numerous CBC20-compliant tokens deployed on the Core network. Different implementations have been crafted by various teams, each with its unique trade-offs, ranging from energy-saving to enhanced security.

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