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Introduction

What is tradeable?​

Tradeable is standard. It describes the interface that enables trading on (some) decentralized exchanges. The idea is to allow other accounts to transfer our assets if we approve them to do so. This concept is mainly used with accounts that are contracts, so they can manage our assets in logic constrained by smart-contract code.

It exposes the same concept of allowance and approval known from ERC20 or ERC721.

When to use?​

If we want to make our asset tradable on platforms, which requires a tradeable interface. Contracts implementing tradeable assets should be composed with other standards like atomic-asset.

Behavior

  • allowance per account can never be < 0

Interface​

transferFrom​

transferFrom(from: string, to: string, amount: uint) => void
  • Transfers amount of tokens from address from to address to.
  • 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 from account has deliberately authorized the sender of the message via some mechanism
  • Transfers of 0 values MUST be treated as normal transfers

approve​

approve(spender: string, amount: uint) => void
  • Allows spender to withdraw from your account multiple times, up to the amount. If this function is called again it overwrites the current allowance with amount
  • To prevent attack vectors like the one described here clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to 0 before setting it to another value for the same spender or use increaseAllowance or decreaseAllowance which are safe. TOUGH The contract itself shouldn’t enforce it

allowance​

allowance(owner: string, spender: string) => {allowance: uint, owner: string, spender: string}
  • view state method - does not modify the state
  • Returns the allowance which spender is still allowed to withdraw from owner

increaseAllowance​

increaseAllowance(spender: string, amountToAdd: uint) => void
  • Increase allowance for spender by given amountToAdd
  • amountToAdd can be equal to zero

decreaseAllowance​

decreaseAllowance(spender: string, amountToSubtract: uint) => void
  • Decrease allowance for spender by given amountToSubtract
  • MUST fail if amountToSubtract > currentAllowance
  • amountToSubtract can be equal to zero