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Contract rules overview

When creating contracts for Sparq, there are a few rules you must follow to ensure they work as intended. While each contract type has its own rules, some other rules apply to both. This will be explained and demonstrated further in the next few subchapters.

General contract rules

As a general stance, contracts must:
  • Inherit from their respective base class, depending on their type (see below) and make sure you're passing the right arguments for their constructors
  • Manage variables within the state and database during contract construction (loading) and destruction (saving)
  • Register callbacks for contract functions with their proper functors/signatures (if functions are called by an RPC eth_call or a transaction)
  • Ensure that their assigned name and their own class name match
    • Both contract constructors take a contractName string as an argument - i.e. if your contract is called "TestContract", your constructor's definition would be TestContract(...) : DynamicContract(interface, "TestContract", ...) - both HAVE to match, otherwise a segfault may happen
  • Declare view functions (functions that do not change state) as const and return a std::string with the encoded ABI (e.g. std::string getBalance(Address add) const { return ABI::Encoder({balance}).getRaw(); })
  • Declare callable functions (functions that do change state and are callable by transactions) as non-const and return void (e.g. void transfer(Address to, uint256_t value) { ... })

Rules for Protocol Contracts

Protocol Contracts specifically must:
  • Inherit BaseContract from src/contract/contract.h:
  • Override ethCall() functions to parse transaction arguments, manage state changes during their processing (depending on whether the call is committing or not), and commit/revert variables when necessary

Rules for Dynamic Contracts

Dynamic Contracts specifically must:
  • Inherit DynamicContract from src/contract/dynamiccontract.h:
  • Override registerContractFunctions() and call it inside the contract's constructor
  • Provide two constructors: one for creating the contract from scratch within ContractManager, and one for loading the contract from the database
  • Only allow contract creation through a transaction call to the ContractManager contract
  • Develop functions for handling your contract's creation and logic
  • Override ethCall() functions to register and properly call those functions
  • Set all of the contract's internal variables as private, inherit them from one of the many Safe Variable classes, and always reference them with this to ensure correct semantics
    • e.g. string name and uint256 value in Solidity should be SafeString name and SafeUint256_t value in C++, respectively - referencing them in your definition would be this->name, this->value...
  • Allow loops using containers such as SafeUnorderedMap, but keep in mind how Safe Containers work
    • e.g. when you access a key from a SafeUnorderedMap, it'll check if it exists and copy only the key, not the entire map or its value - thus when iterating a loop, you can't assume the "temporary" value is the original one
    • We recommended you only loop inside view functions to ensure value safety, but you can do it on non-view functions as well, just be careful when doing so
  • Trigger state changes only via transaction calls to contract functions
  • Call updateState(true) at the end of the contract's constructor

Global Contract Variables

For both contract types (Protocol and Dynamic), you can use the following global functions during an ethCall():
Global Function
return type
Returns the contract's address
Returns the contract's owner
Returns the contract's chainId
Returns the contract's name
Returns the transaction's origin
Returns the transaction's caller
Returns the transaction's value
Returns if the call is committing to state
For Dynamic Contracts specifically, you can also use the following global functions:
Global Function
return type
const getContract(address)
Returns a contract of type T
const T
callContract(address, ABI, callValue)
Calls contract function
Get the current balance of an address
sendTokens(address, value)
Send tokens to an address