How to download and setup qt-promise
Open terminal and run command
                                            git clone https://github.com/bwalter/qt-promise.git
                                        
                                        git clone is used to create a copy or clone of qt-promise repositories.
                                        You pass git clone a repository URL. it supports a few different network protocols and corresponding URL formats.
Also you may download zip file with qt-promise https://github.com/bwalter/qt-promise/archive/master.zip
Or simply clone qt-promise with SSH
                                            [email protected]:bwalter/qt-promise.git                                    
                                    If you have some problems with qt-promise
You may open issue on qt-promise support forum (system) here: https://github.com/bwalter/qt-promise/issuesSimilar to qt-promise repositories
Here you may see qt-promise alternatives and analogs
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