Migrating from Solidity++ 0.4

Comparing with Solidity++ 0.4, Solidity++ 0.8 is much syntactically closer to Solidity, which makes it more friendly to developers who want to migrate from Solidity.

Note: Some counter-intuitive syntax and keywords are removed in this version.

Solidity++ 0.8.0

Breaking Changes

• All Solidity breaking changes since v0.4.3 to v0.8.0 are applied to Solidity++ 0.8.0.
• Most of Solidity contracts and libraries can be compiled by solppc 0.8.0 and imported by Solidity++ 0.8.0 contracts, except for the contracts with external / delegate calls.
• onMessage keyword is deprecated since 0.8.0. Use function declarations instead.
• message keyword is deprecated since 0.8.0. Use function declared in a contract or interface instead.
• send keyword is deprecated since 0.8.0. Use function calls instead.
• getter keyword is deprecated since 0.8.0. Use view/pure functions instead.
• Inline assembly and Yul are supported since 0.8.0.
• keccak256 is available since 0.8.0.
• tokenId keyword (Vite Native Token Id type) is changed to vitetoken.
• Some transaction properties are changed since 0.8.0: msg.tokenid is changed to msg.token, msg.amount is changed to msg.value.

Compatibilities

• An external or public function (without return values) in 0.8.0 equivalents to onMessage in 0.4.3. They have the same signature and selector. For example function set(uint data) external equivalents to onMessage set(uint data).
• An external or public function declaration in 0.8.0 equivalents to message declaration in 0.4.3.
• A contract compiled by solppc 0.8.0 can call contracts compiled by solppc 0.4.3 asynchronously.
• A contract compiled by solppc 0.4.3 can call contracts compiled by solppc 0.8.0 asynchronously.
• The ABI encoding, storage layout, memory layout and calldata layout remain unchanged.

Solidity++ 0.8.1

Breaking Changes

• Solidity contracts and libraries with external / delegate calls can be compiled by solppc 0.8.1 and imported by Solidity++ 0.8.1 contracts.
• await operator is introduced since 0.8.1.
• Error propagation through revert and try/catch is enabled since 0.8.1.
• Delegate calls are allowed since 0.8.1.
• External / delegate calls in Solidity are allowed since 0.8.1.
• Library linking and calls to external library functions are allowed since 0.8.1.

Compatibilities

• A contract compiled by solppc 0.8.1 can call contracts compiled by solppc 0.4.3 asynchronously.
• A contract compiled by solppc 0.8.1 can call contracts compiled by solppc 0.8.0 both synchronously and asynchronously.
• A contract compiled by solppc 0.8.1 can get return values after a synchronous call to a contract compiled by solppc 0.8.0.
• The ABI encoding, storage layout, memory layout and calldata layout remain unchanged.

Migrate to 0.8.0

Let's start with an example:

Copy 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 { address addrA; uint total; message add(uint a, uint b); constructor (address addr) { addrA = addr; } onMessage invoke(uint a, uint b) { send(addrA, add(a, b)); } onMessage sum(uint result) { total += result; } getter total() returns(uint) { return total; } getter getSomething() returns(uint) { return total + 1; } }

In above code, contract A declares a message listener add(uint a, uint b).

contract B declares add message which has the same signature to add message listener in contract A.

Contract B declares a message listener invoke as the entry to the contract. When B.invoke() is called, contract B sends a add message to contract A to initiate an asynchronous message call.

When contract A responds to the message call, it sends a sum message back to contract B to return data asynchronously.

Contract B also declares a message listener sum(uint result) as a 'callback function' to handle the returned message from contract A.

Since 0.8.0, onMessage and message are replaced with function, send statements are replaced with function calls. The await operator is not available in 0.8.0, it is required to declare callbacks explicitly using function.

The migrated code in 0.8.0 is as follows:

Copy // SPDX-License-Identifier: GPL-3.0 pragma soliditypp ^0.8.0; interface Listener { // delare a callback to receive the result function sum(uint result) external; } contract A { // the onMessage is replaced with an external function function add(uint a, uint b) external { Listener sender = Listener(msg.sender); // send message to the caller sender.sum(a + b); } } contract B is Listener { A contractA; uint public total; // a getter function will be auto-generated by the compiler constructor (address addr) { contractA = A(addr); } // the onMessage is replaced with a function function invoke(uint a, uint b) external { // replace the send statement with a function call contractA.add(a, b); } // the callback is replaced with a function function sum(uint result) external override { total += result; } // the offchain getter is replaced with a view or pure function function getSomething() external view returns(uint) { return total + 1; } }

Migrate to 0.8.1

Since Solidity++ 0.8.1, no explicit callback declarations are required.

The compiler is smart enough to generate callbacks automatically. The code is cleaner and optimized significantly by the introduction of await.

The migrated code in 0.8.1 is as follows:

Copy // SPDX-License-Identifier: GPL-3.0 pragma soliditypp ^0.8.1; contract A { // the async function can return data to the caller function add(uint a, uint b) external async returns(uint) { return a + b; } } contract B { A contractA; uint public total; constructor (address addr) { contractA = A(addr); } function invoke(uint a, uint b) external async { // use await expression to get data returned from the called contract total += await contractA.add(a, b); } function getSomething() external view returns(uint) { return total + 1; } }