# 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.

WARNING

Message listeners cannot be called directly as normal functions.

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);
     }
}

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