How new fungible token is minted?

tahlil · February 6, 2024, 1:26pm

When I mint A fungible token is a new object created or has the property of the fungible token object (like address to balance mapping) changed?

amnn · February 7, 2024, 4:51pm

Hi @tahlil, the answer is (kind of) both!

If you mint a new Coin<C> for some type C that you own the TreasuryCap<C> for, you will both get a new Coin<C> object and you will update the total supply field in TreasuryCap<C>. This is done using coin::mint:

github.com

MystenLabs/sui/blob/8ce29fe3fd12834a07ff024f01350bbc7a110a7c/crates/sui-framework/packages/sui-framework/sources/coin.move#L261-L270


      
          /// Create a coin worth `value`. and increase the total supply
          /// in `cap` accordingly.
          public fun mint<T>(
              cap: &mut TreasuryCap<T>, value: u64, ctx: &mut TxContext,
          ): Coin<T> {
              Coin {
                  id: object::new(ctx),
                  balance: balance::increase_supply(&mut cap.total_supply, value)
              }
          }

There’s also a variant of this function – coin::mint_balance – which updates the total supply field, but creates a Balance<C> value, instead of Coin<C>, which is not an Object. You can later convert that balance into a coin, if you like.

Note that the only thing that we are updating in the centralised TreasuryCap<C> is the total supply – there is no global address to balance mapping.