I was following this guide:

Configuring Genesis for Balances


but got this error:

associated type Balance not found for T, associated type Balance not found

So where/what is the definition for this?

I think it is somewhere inside https://docs.substrate.io/rustdocs/latest/pallet_balances/index.html

I tried this: type Balance: balances::Config::Balance;

then failed: expected trait, found associated type balances::Config::Balance not a trait

Please advise. Thank you

1 Answer 1


Substrate chains are designed to be completely modular and without any assumptions about the underlying blockchain. This means that Balances are not necessarily a first class citizen within your runtime. Instead, if you want to use Balances in your chain, you need to follow a few common steps which you will see in most pallets.

  1. Configure your chain to use a Currency:

    pub trait Config: frame_system::Config {
        /// Currency type for this pallet.
        type Currency: ReservableCurrency<Self::AccountId>
            + LockableCurrency<Self::AccountId, Moment = Self::BlockNumber>;
        // ...

    Note you may not need both ReservableCurrency and LockableCurrency, it depends on how you want to play with the currency.

  2. Create a simple type alias to make it easier to access the Balance type inside of Currency:

    type BalanceOf<T> =
        <<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance;
  3. Use this type alias wherever you want to use the Balance type:

    fn transfer(to: T::AccountId, from: T::Account, amount: BalanceOf<T>) -> DispatchResult { ... }

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