Playground.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.13;

import {Router} from "@abacus-network/app/contracts/Router.sol";

contract Playground is Router {

    constructor(address abacusConnectionManager_) {
        __AbacusConnectionClient_initialize(abacusConnectionManager_);
    }

    string public message;

    function foo(uint32 destination_, string memory message_) external {
        _dispatch(
            destination_,
            abi.encodeWithSelector(
                this.handleBar.selector,
                message_
            )
        );
    }

    function _handle(uint32 origin_, bytes32 sender_, bytes memory message_) internal virtual override {
        // is origin_ / sender_ validated / guaranteed to be correct?
        address(this).call(message_);
    }

    function handleBar(string memory message_) external onlyInbox {
        message = message_;
    }
}