# Solidity++

Solidity++ retains most syntax of Solidity. However, Solidity++ is still a different language. The difference mainly lies in asynchronous design.

# Syntax Removed in Solidity++

Below syntax has been removed from Solidity

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

Syntax related to ecrecover and ripemd160 has been disabled

DELEGATECALL is not available in Solidity++ at this moment

Syntax of inline assembly in Solidity is temporarily unavailable

# Syntax Added/Modified in Solidity++

Below syntax has been added in Solidity++

bytes32 b1 = fromhash();
uint height = accountheight();
bytes32 b2 = prevhash();
uint64 random = random64();

• fromhash() returns request transaction's hash

• accountheight() returns latest block height of an account

• prevhash() returns latest block hash of an account

• random64() returns a random number in uint64 . This function will return the same random number in one transaction

• nextrandom() returns a random number in uint64 . This function can be called multiple times to obtain different random numbers in one transaction

Functions address and tokenId are redefined in Solidity++:

tokenId token01 = tokenId("tti_2445f6e5cde8c2c70e446c83");
tokenId token02 = "tti_2445f6e5cde8c2c70e446c83";
address addr01 = address("vite_0102030405060708090807060504030201020304eddd83748e");
address addr02 = "vite_0102030405060708090807060504030201020304eddd83748e";

Obtain transfer value in Solidity:

msg.value

Obtain transfer value in Solidity++( value has been changed to amount ):

msg.amount;

Obtain transfer token id(Solidity doesn't have the feature):

msg.tokenid;

Obtain account balance in Solidity:

address.balance

Obtain account balance in Solidity++(a parameter of tokenId is required):

address.balance(_tokenId)

In Solidity, send ETH to an address:

address(_addr).transfer(_amount);

In Solidity++, send specific token to an address:

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++

Unlike Solidity, in-contract communication in Solidity++ is not done through function calls, but by message passing

In Solidity++,

• public functions cannot be accessed from outside of the contract
• function cannot be declared as external . Instead, function can only be declared as public , private or internal
• public static variable is not visible from outside of the contract

An example

pragma soliditypp ^0.4.3;
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);
    onMessage invoker(address addr, uint a, uint b) {
       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. In above example, message sum(uint result) declares message "sum" accepting a uint parameter.

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

• send : keyword, sending a message, accepting two parameters including message receiving address and message body

Message can be declared in contract and can only be sent out from the exact contract who declares it. If a message should be processed by another contract, the name and passed-in parameters of the message rely on how message listener is defined in the other contract.

In other words, if contract A would like to send a message to contract B, A must define the message in a format that complies to the listener defined in contract B.

Message listener is defined in contract. A message listener specifies a certain type of message that can be processed by the contract. Unrecognized messages will not be handled but discarded.

In above example,

Contract A defines a message listener add(uint a, uint b) while contract B defines sum(uint result) , indicating the messages that can be processed by contract A or contract B.

Here contract B sends message to contract A. For this purpose, contract B must declare "add" message which complies to add(uint a, uint b) defined in contract A. Similarly, contract A should declare "sum" message matching message listener sum(uint result) of contract B, since contract A will send such a message to contract B in return.

# getter in Solidity++

In Solidity++, because interactions between contracts are carried out through asynchronous messaging, the public fields cannot be accessed directly from outside of the contract. To address this problem, Solidity++ provides a solution.

pragma soliditypp ^0.4.3;
contract A {
    uint magic = 0;
    getter getMagic() returns(uint256) {
        return magic;
    }
    getter getMagicAdd(uint256 m) returns(uint256) {
        return calculate(m);
    }
    function calculate(uint256 m) public view returns(uint256) {
        return m + magic;
    }
}

As shown in above example, a "getter" method getMagic() is defined to access public field magic . In general, "getter" in Solidity++ has the following characteristics:

• Keyword getter is used to declare such a method.
• Method name, input parameters and return value are required. As query method, it is only used to obtain the specific field's value and cannot modify it.
• The compiled code of "getter" is not stored on chain, so it is not allowed to access transaction related information, such as msg.amount or msg.tokenid , within "getter".
• "getter" cannot send transactions or send messages. It cannot call require or revert either.
• "getter" can call functions, which should be defined as view type.

# Example of Solidity++ Contract

Below contract defines a batch transfer which accepts a list of addresses and amounts and then transfers specified amount to specified address in the list

// Declare the contract is written in soliditypp 0.4.3. Backwards compatibility is guaranteed for generating the same compiling result.
pragma soliditypp ^0.4.3;
// Define contract A
contract A {
     // Define a message listener. Every external method should be defined as message listener in Solidity++
     // Define listener name and parameters. Visibility is not necessary. Message listener has no return value
     // Messsage listener "transfer" is defined with a passed-in parameter of a uint array, in format of address in odd element and amount in even
     onMessage transfer(uint[] calldata body) payable {
         // Check if the parameter length is even because each address should have corresponding 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) {
                // Transfer to address
                address(addr).transfer(msg.tokenid, amount);
             }
         }
         require(totalAmount == msg.amount);
     }
}