EVM Precompiled Contracts
Precompiles in Solidity is a native way to speed up general but expensive functions and interacts with something outside the VM. For example, ECRecover precompiled smart contracts definitely boost public key recovery functions because of execution almost on the hardware level. From another side, the Plasm Network includes dispatch precompiled smart contracts, that permit Solidity developers to interact with other Plasm runtime modules.
The ECRecover is a standard Solidity precompiled smart contract available at the address 0x01. It is used in most contracts to improve ECDSA performance during recovering signature signer account.
On standard Plasm Parachain runtime Dispatch smart-contract available at the address:
0x0000000000000000000000000000000000000006
Internally, this contract just decodes input data as Call structure
let call = T::Call::decode(&mut &input[..]).map_err(|_| ExitError::Other("decode failed".into()))?;
and then executes it as a transaction from smart contract origin.
let origin = T::AddressMapping::into_account_id(context.caller);match call.dispatch(Some(origin).into()) {...
That means each EVM smart contract could call any available method of runtime using Solidity standard call() function to the precompiled contract address.
The difficulty for Solidity developers is that the SCALE codec isn't available for Solidity. As a result, they should encode call parameters manually that could be complex and expensive.
But for calling standard or trivial methods it's not a big problem. For example, call Balances::transfer() for 5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty and 42 looks like:
0x0400008eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48a8
Where 0x04 is a module index, following 0x00 is a method index in the module and next is address and balance parameters. If your contract should constantly transfer the same amount to the same destination, then a constant call string could be used.
