What is the TL-B scheme in ton-solidity and how to use it?

Question

This question is about ton-solidity language of Everscale blockchain smart contracts.

Sometimes, I see the code relative to TL-B scheme. For example, like this:

function getInvokeMessage(address sender, address recipient, uint128 amount, bool bounce, TvmCell payload) public pure
        returns(TvmCell message) {
        TvmCell body = tvm.encodeBody(MsigDebot.invokeTransaction, sender, recipient, amount, bounce, payload);
        TvmBuilder message_;
        message_.store(false, true, true, false, address(0), address(this));
        message_.storeTons(0);
        message_.storeUnsigned(0, 1);
        message_.storeTons(0);
        message_.storeTons(0);
        message_.store(uint64(0));
        message_.store(uint32(0));
        message_.storeUnsigned(0, 1); //init: nothing$0
        message_.storeUnsigned(1, 1); //body: right$1
        message_.store(body);
        message = message_.toCell();
    }

I need explanations step by step, what does this code doing? Or give me the refers to documentation that explain it.

Answer 1

The messages construct accordingly to TL-B scheme.

In general, the message has type that called "Message X"

This type has 3 parts.

The first part is the "CommonMsgInfo"

           /* int_msg_info$0
           ihr_disabled:Bool
           bounce:Bool
           bounced:Bool
           src:MsgAddressInt
           dest:MsgAddressInt */
        message_.store(false, true, true, false, address(0), address(this));
        message_.storeTons(0);//value:CurrencyCollection
        message_.storeUnsigned(0, 1);//value:CurrencyCollection (for other currencies)
        // In the next 4 fields we store zeroes, because blockchain software will replace them
        // with the correct values after this function finishes execution.         
        message_.storeTons(0);//ihr_fee:Grams
        message_.storeTons(0);//fwd_fee:Grams
        message_.store(uint64(0));//created_lt:uint64
        message_.store(uint32(0));//created_at:uint32

The second part has type "init"

        message_.storeUnsigned(0, 1); //no initial state

The third part has type "body"

        message_.storeUnsigned(1, 1); //1 because, we don't store body in current cell
        message_.store(body);