如何为 Substrate Runtime 实现 EVM Trait？

Question

Following the adding a module to your runtime , I'm trying to implement the Parity Substrate paint-evm trait for the Dothereum Runtime .

TheEVM module trait is defined as follows:

pub trait Trait: Trait + Trait {
    type FeeCalculator: FeeCalculator;
    type ConvertAccountId: ConvertAccountId<Self::AccountId>;
    type Currency: Currency<Self::AccountId>;
    type Event: From<Event> + Into<Self::Event>;
    type Precompiles: Precompiles;
}

The adding a module tutorial here, however, is a bit vague and encourages one to:

".. explore the source code of the [..] module if things don't make sense.."

While the EVM module code doesn't seem too complex, I fail to understand how to implement the EVM trait for my runtime:

impl evm::Trait for Runtime {
    type FeeCalculator = ();
    type ConvertAccountId = ();
    type Currency = Balances; 
    type Event = Event;
    type Precompiles = ();
}

What types do FeeCalculator and ConvertAccountId expect here?

Answer 1

Because pallet-evm doesn't provide default implementations for the types you need, you'll need to create them yourself.

use paint_evm::{FeeCalculator, ConvertAccountId};
use primitives::{U256, H160};

pub struct FixedGasPrice;

impl FeeCalculator for FixedGasPrice {
    fn gas_price() -> U256 {
        // Gas price is always one token per gas.
        1.into()
    }
}

pub struct TruncatedAccountId;

impl<AccountId> ConvertAccountId<AccountId> for TruncatedAccountId {
    fn convert_account_id(account_id: &AccountId) -> H160 {
        //TODO just truncate the fist several bits and return the resulting H160
        // Or maybe hashing is easier to figure out
        unimplemented!();
    }
}

impl paint_evm::Trait for Runtime {
    type FeeCalculator = FixedGasPrice;
    type ConvertAccountId = TruncatedAccountId;
    type Currency = Balances;
    type Event = Event;
    type Precompiles = (); // We can use () here because paint_evm provides an
                           // `impl Precompiles for ()``
                           // block that always returns none (line 75)
}

I look forward to improving this answer as I understand more myself.