# Solidity++

Solidity++ retains most syntax in Solidity. The difference mainly comes from Vite's asynchronous architecture and native multi-token model, as explained below.

# Syntax Removed in Solidity++

tx.gasprice
block.coinbase
block.difficulty
block.gaslimit
gasleft()
msg.gas
selfdestruct(_owner)
suicide(_addr)
address(_addr).send(_amount)

Above syntax has been disabled in Solidity++

Syntax related to ecrecover and ripemd160 has been disabled

DELEGATECALL is not available at this moment

# Syntax Added/Modified in Solidity++

address and tokenId are redefined in Solidity++

tokenId token01 = tokenId("tti_2445f6e5cde8c2c70e446c83");
tokenId token02 = "tti_2445f6e5cde8c2c70e446c83";
address addr01 = address("vite_8ba849f3678057aeefc84c787f7cb957426cc3a4b0e8eca13c");
address addr02 = "vite_8ba849f3678057aeefc84c787f7cb957426cc3a4b0e8eca13c";

To obtain transfer tokenId in Solidity++

msg.tokenid

To obtain account balance

In Solidity,

address.balance

In Solidity++, since multiple tokens co-exist in an account, a parameter of tokenId is required

address.balance(_tokenId)

In Solidity, sending ETH to an address

address(_addr).transfer(_amount);

In Solidity++, sending token to an address. An additional parameter of tokenId is required

address(_addr).transfer(_tokenId, _amount);

Unit of ETH in Solidity: wei/szabo/finney/ether

1 ether = 1000 finney, 1 finney = 1000 szabo, 1 szabo = 1000000000000 wei

Unit of VITE in Solidity++: attov/vite

1 vite = 1000000000000000000 attov

In Solidity++, all syntax related to sha256 or sha3 is replaced by blake2b

# Asynchronous Syntax in Solidity++

In Solidity++, cross-contract calls are not completed by function calls, but only by message sending

public function in Solidity++ won't provide external access. Moreover, function is not be able to declare as external. Instead, function can only be declared as public, private or internal

In the meantime, public static variable can not be visited from outside

An example

pragma soliditypp ^0.4.0;
contract A {
   message sum(uint result);

   onMessage add(uint a, uint b) {
        uint result = a + b;
        address sender = msg.sender;
        send(sender, sum(result));
   }
}
contract B {
    uint total;
    message add(uint a, uint b);

    function invoker(address addr, uint a, uint b) public {
       send(addr, add(a, b));
    }

    onMessage sum(uint result) {
        if (result > 10) {
           total += result;
       }
    }
}

message: keyword, declaring a message, including message name and passed-in parameter. message sum(uint result) declares message "sum", accepting a uint parameter.

onMessage: keyword, declaring a message listener, including message name, passed-in parameter and logic that handles the message. onMessage add(uint a, uint b) declares message listener "add", accepting two uint parameters.

send: keyword, sending a message, accepting two parameters, the message receiving address and the actual message

Messages can be declared in contract. The send operation of the message can only be called in the contract that declares it. If a message is to be processed by another contract, the name and passed-in parameters of the message rely on how message listener defines in the other contract.

In other words, if contract A is going to send a message to contract B for processing, contract B must define a listener of a certain type of message for A to follow when declaring the message.

A contract can define a message listener. The message listener specifies the type of message that the contract can receive. Only messages that conform to spec will be normally received and processed.

Note: message listener cannot be called directly like normal function.

In above example,

Contract A defines message listener add(uint a, uint b) while contract B defines message listener sum(uint result), indicating contract A and contract B will receive the two kinds of messages and process respectively.

Since contract B sends message to contract A, contract B must declare an "add" message which complies to the message listener defined in contract A. Meanwhile, contract A should declare a "sum" message according to the message listener in contract B, since contract A will send "sum" message to contract B in message listener "add".

# Example of a Solidity++ Contract

A batch transfer contract which accepts a list of addresses and amounts and transfers the specified amount to the specified address

// Declares the contract is written in soliditypp 0.4.0. Backwards compatibility is guaranteed to ensure different version of compilers will yield the same output.
pragma soliditypp ^0.4.0;
 
 
// Defines contract A
contract A {
     // Defines a message listener. Since cross-contract communication has to be completed via message sending, all external methods must be defined as message listeners
     // The listener needs to define message name and parameters. Visibility is not necessary. Message listener has no return value
     // In this example, a "transfer" listener is defined with a passed-in parameter of uint array, representing address in odd element and amount in even
     onMessage transfer(uint[] calldata body) payable {
         // Checks if the parameter length is even because each address has to match an amount
         require(body.length%2==0);
         uint256 totalAmount = 0;
         for(uint i = 0; i < body.length; i=i+2) {
             uint addr = body[i];
             uint amount = body[i+1];
             totalAmount = totalAmount + amount;
             require(totalAmount >= amount);
             if(amount > 0) {
                // Transfers the amount to address. Token ID is defined in msg.tokenid
                address(addr).transfer(msg.tokenid ,amount);
             }
         }
         require(totalAmount == msg.value);
     }
}