This repository is an attempt to successfully compile and test the JacopoMangiavacchi / SwiftPlusPlus package which provides a Swift Wrapper, calling a C Wrapper, calling a C++ wrapper, calling STL with Swift Package Manager (Linux).

Please see full instruction at https://medium.com/@JMangia/swift-swift-c-c-stl-9e620e471145

Highlight from Jacopo Mangiavacchi's Medium post "Swift++ == Swift => C => C++ => STL" are noted below.

At this point in time, the package builds without errors. However, the test fails with the following errors.

Linux, Swift 5.1-dev installed, using Swift 4.2 in package

XCTAssertEqual failed: ("Optional("\0")") is not equal to ("Optional("0")")
XCTAssertEqual failed: ("Optional("0")") is not equal to ("Optional("2")")

macOS, Swift 5.0.1 installed, using Swift 4.2 in package

XCTAssertEqual failed: ("Optional("p")") is not equal to ("Optional("0")")
XCTAssertEqual failed: ("Optional("p")") is not equal to ("Optional("2")")

Swift Package supports for C language can directly import C Libraries (.so or .dylib). However, C++ class interaction are not a simple a C library interaction.

This package creates a Swift wrapper for the famous C++ stl::list template class. In particular, first a C++ Wrapper is created, then a C Wrapper and finally the Swift Wrapper. The goal is to recreate an interface similar to the original C++ code.

The constructs void * in C++ and Data in Swift are used to be as generic as possible.

The CPPListIterator and CPPListWrapper C++ wrapper classes define the interfaces for the std::iterator and std::list classes in the standard C++ STL library.

Given the C++ class hierarchy to export in Swift, the next step to do is to de-objectify all the C++ interfaces and create a simple extern "C" interface, in C++.

The exporting C methods wrap access to the this C++ instance with a void * object. The void * object is always passed as first parameter to all C interface methods.

Given the de-objectified C interface, then Swift classes with behaviors similar to the original C++ classes can created. Alternately, a more "Swifty" wrapper can be created for the Swift side.

This example strives to similitude the original C++ interface as much as possible.

There is some complexity dealing with data conversion and memory management converting data from the Swift world to the void * generic pointers for the C++ stl::list implementation. Swift Data is used instead of String to keep the example more general. In this case, the Swift Data is converted back and forward to UnsafeRawPointer in order to pass a void * pointer.

Finally in order to put all the C++, C and Swift source code in a unique project and just build everything with the swift build tool here are some advise about to easily manage your project subfolders and the main Swift Package file.

The subfolder organization used places CPPListWrapper within the CListWrapper. For simplicity the C++ Wrapper code in a separate (CPPListWrapper) subfolder, but this is not strictly needed.

This folder structure allows Package.swift to directly point to your C, and included C++. The include subfolder under the C wrapper folder (CListWrapper) enables a module.modulemap file to be automatically generated. Note that CListWrapper.cpp needs to state the include/ directory path #include "include/CListWrapper.hpp".

tree Sources/
# Sources/
# |-- CListWrapper
# |   |-- CListWrapper.cpp
# |   |-- CPPListWrapper
# |   |   |-- CPPListWrapper.cpp
# |   |   `-- CPPListWrapper.hpp
# |   `-- include
# |       `-- CListWrapper.hpp
# `-- SwiftPlusPlus
#     `-- SwiftPlusPlus.swift

Use the -std=c++11 flag in the swift build command to enable C++ 11 features.

# build:
swift build -Xcxx -std=c++11

# build release:
swift build --configuration release -Xcxx -std=c++11

# test:
swift test -Xcxx -std=c++11

# run:
swift run -Xcxx -std=c++11

• GitHub/JacopoMangiavacchi: SwiftPlusPlus
• Medium: Jacopo Mangiavacchi
  • Swift++ == Swift => C => C++ => STL published Mar 16, 2018.