Expand the Swift overlay for the C++ Standard Library

AbdoGad · February 15, 2023, 8:04pm

Hi @egor.zhdan ,
I am Abd al Rahman Gad,
I am a second year computer science student,
I have a good understanding of c++ and a deep understanding of the standard template library such as( vector , set , map ,etc… and the functions in std::algorithm) because of my use of them in problem solving in various websites and I am interested in participating in the “Expand the Swift overlay for the C++ Standard Library” project .

I have seen the resources you’ve listed in the reply here :

Especially this :

github.com

apple/swift/blob/main/docs/CppInteroperability/CppInteroperabilityManifesto.md

# Interoperability between Swift and C++

# ⚠️ Warning: document is out of date. ⚠️

**This document has not had significant updates in the last three years. The goals and design outlined here do not necessarily reflect those established by the C++ Interop Work Group. For an up-to-date document, please see [the Forward Vision document](https://github.com/apple/swift-evolution/blob/main/visions/using-swift-from-c%2B%2B.md).**

[** ‼️ Additionally, the official C++ interoperability documentation is live at Swift.org and provides an up-to-date guide for mixing Swift and C++ ‼️ **](https://www.swift.org/documentation/cxx-interop/)

This document discusses the design and tradeoffs for bidirectional API-level
interoperability between Swift and C++.

Assumptions:

* We can make changes to the Swift language and the standard library.
  * The proposed changes must fit Swift's goals and philosophy. In other words,
    the proposed changes must have a reasonable chance to be accepted by the
    Swift community. For example, a change that requires an ABI break on Apple
    platforms is a non-starter.
  * Forking the Swift language or standard library, or creating a dialect
    without a fork (and therefore, being able to make radical changes to Swift's

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and this :

github.com

apple/swift/blob/main/docs/CppInteroperability/CppInteroperabilityStatus.md

[** ‼️ The official C++ interoperability documentation and status page is live at Swift.org and provides an up-to-date guide for mixing Swift and C++ ‼️ **](https://www.swift.org/documentation/cxx-interop/status)

#  C++ Interoperability Status

Swift has some experimental ability to interoperate with C++.
This document provides an overview of the status of the Swift and C++ interoperability support.

## C++ to Swift Interoperability Status

Swift has the experimental ability to import a large subset of C++.
This section of the document describes which C++ language and standard library features can be imported and used from Swift in an experimental manner.

### Example
The following example demonstrates several interop features. It compiles and runs on main.

```C++
// cxx-types.h (mapped to CxxTypes module in module.modulemap)
#include <algorithm>
#include <vector>

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I have also seen the “How Swift imports C APIs” right here :

github.com

apple/swift/blob/main/docs/HowSwiftImportsCAPIs.md

# How Swift imports C APIs

When Swift imports a module, or parses a bridging header from a C-based language
(C, Objective-C), the APIs are mapped into Swift APIs and can be used directly
from Swift code. This provides the basis for Swift's Foreign Function Interface
(FFI), providing interoperability with existing libraries written in C-based
languages.

This document describes how APIs from C-based languages are mapped into Swift
APIs. It is written for a broad audience, including Swift and C users who
might not be language experts. Therefore, it explains some advanced concepts
where necessary.

* [Names, identifiers and keywords](#names-identifiers-and-keywords)
  * [Unicode](#unicode)
  * [Names that are keywords in Swift](#names-that-are-keywords-in-swift)
  * [Name translation](#name-translation)
  * [Name customization](#name-customization)
* [Size, stride, and alignment of types](#size-stride-and-alignment-of-types)
* [Fundamental types](#fundamental-types)

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I now have a good idea about the project and the general desired deliverables of it , this project had my interest and I really want to be part of it.

here are some questions I want to ask to get better understanding of the project :

1- what is the exact deliverables that we want to accomplish in Gsoc 2023 ?
2- how should I prepare for the project ( resources , advises , etc..) to become a better candidate and hopefully be chosen ?

egor.zhdan · February 16, 2023, 9:08pm

Hi, it's great to see that you're interested in the project and already looked into the docs for the C++ stdlib overlay!

An example of what could be implemented as part of this project is conversion mechanisms between C++ standard library types and Swift standard library types. The overlay already provides a conversion mechanism between C++'s std::string and Swift's String. This is quite useful in cases where e.g. a C++ library exposes a function that takes an instance of std::string as a parameter, and a Swift developer wants to call this function from Swift. Here is how the conversion is currently implemented: https://github.com/apple/swift/blob/9bdbd38a3c63872e90ccadc27def1569a49fff2a/stdlib/public/Cxx/std/String.swift#L13-L24.
We don't want to limit the contributions to this specific part of the overlay, so if you have other ideas on how the overlay could be improved, please feel free to propose those!

One way to become more familiar with the project would be to try and build Swift, including the overlay, locally. Here are some docs on building Swift: https://github.com/apple/swift/blob/main/docs/HowToGuides/GettingStarted.md#the-actual-build.
Once you know how to build Swift, you could try making a small change to the overlay, and then rebuilding Swift to see how your change looks in an actual Swift toolchain. That would help you to get started with contributing to the overlay, and to the Swift project in general.

Feel free to ask me any questions!