# Amounts, Values, and Brands

# Amounts

Amount methods

Amounts describe digital assets. There are no amount API methods. Instead, an amount has two properties, value and brand with their own API methods. Use the amountMath API methods (covered in-depth here) to get information about and otherwise manipulate an amount as a whole. amountMath.make() is generally how you make new amounts.

However, you can also make an amount as an object literal by making a record of a brand and a value. While amountMath.make() is recommended for proper object-oriented programming (it also checks the brand's validity), this produces the same result:

  const newAmount = { brand: quatloosBrand, value: 5 };

amount has two properties:

  • Brand: The kind of digital asset, such as our imaginary Quatloos currency or, in a game, a powerful magic sword with a brand of Plus3Sword-ABCGames or similar.
  • Value: How much/many of the asset. Fungible values are natural numbers. Non-fungible values may be represented as strings naming a particular right, or an arbitrary object representing the rights at issue (e.g., a theatre ticket's date, time, row and seat positions).

amounts and their values and brands are manipulated by the AmountMath API. It executes the logic of how amounts change when digital assets are merged, separated, or otherwise manipulated. For example, you make an offer for something, which is declined. You want to change your offer, represented as an amount, to be of a greater value by adding to it.

# Brands

Brand methods

A brand object is an amount object's kind of digital asset, such as our imaginary Quatloos currency or, in a game, a powerful magic sword.

In ERTP, mint objects create new asset payment objects. Each mint has a one-to-one relationship with an issuer object. And each issuer object has a one-to-one relationship with a brand object. This means:

  • A mint can only create a payment for one specific brand, which must be the same brand as their associated issuer.
  • An issuer can only create a new empty purse for one specific brand.
  • An amount is either fungible or non-fungible, as determined by which its issuer, and thus its brand, was created to be.

A brand has two associated methods. The following is a brief description and example of each brand method. For more detail, click the method's name to go to its entry in the ERTP API Reference.

  • brand.isMyIssuer(issuer)
    • Returns true if the issuer argument matches the issuer associated with the brand. We have this method because the issuer is authoritative and the brand is not. You can create a payment, purse, or amount with a brand that claims a particular issuer, without that issuer having been involved. But if you use that payment or purse, it won't be accepted by genuine ones. So to know, you have to verify with the issuer to see if it agrees.
    •   const isIssuer = brand.isMyIssuer(issuer);
  • brand.getAllegedName()
    • Return the brand's alleged name, but should not be trusted as accurate.
    •   const name = brand.getAllegedName();

The following methods on other ERTP components also either operate on or return a brand.

  • issuer.getBrand()
    • Returns the brand for the issuer. The brand is not closely held, so this should not be trusted to identify an issuer alone. Fake digital assets and amounts can use the brand of another issuer.
    • const myBrand = quatloosIssuer.getBrand();
      // myBrand === quatloosBrand
  • payment.getAllegedBrand()
    • Return the payment's alleged brand. Because a payment is not trusted, this should be treated with suspicion and verified elsewhere. This example code determines if a payment we got from untrusted sources is valid. It uses the brand to find a purse we want to deposit it in, then verifies that it's genuine.
    • const allegedBrand = payment.getAllegedBrand();
      const probablyAppropriatePurse = brandToPurse.get(allegedBrand);
      const depositAmount = probablyAppropriatePurse.deposit(payment);
  • amountMath.getBrand()
    • Return the brand the amountMath object is using for its methods.
    •   const newBrand = quatloosAmountMath.getBrand();

# Values

Value methods

Values are the "how many" part of an amount. There are no value methods, but two amountMath methods use or return them.

  • amountMath.getValue(amount)
    • Return the amount argument's value
    • const quatloos123 = quatloosAmountMath.make(123);
      // returns 123
      const value = quatloosAmountMath.getValue(quatloos123);
  • amountMath.make(allegedValue)
    • Make an amountfrom a value by adding the amountMath associated brand to the value.
    •   const quatloos837 = quatloosAmountMath.make(837);