GSL/README.md

# GSL: Guidelines Support Library
[![Build Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL) [![Build status](https://ci.appveyor.com/api/projects/status/github/Microsoft/GSL?svg=true)](https://ci.appveyor.com/project/neilmacintosh/GSL)

The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
[C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines) maintained by the [Standard C++ Foundation](https://isocpp.org).
This repo contains Microsoft's implementation of GSL.

The entire implementation is provided inline in the headers under the [gsl](./include/gsl) directory. The implementation generally assumes a platform that implements C++14 support.

While some types have been broken out into their own headers (e.g. [gsl/span](./include/gsl/span)),
it is simplest to just include [gsl/gsl](./include/gsl/gsl) and gain access to the entire library.

> NOTE: We encourage contributions that improve or refine any of the types in this library as well as ports to
other platforms. Please see [CONTRIBUTING.md](./CONTRIBUTING.md) for more information about contributing.

# Project Code of Conduct
This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.

# Usage of Third Party Libraries
This project makes use of the [Google Test](https://github.com/google/googletest) testing library. Please see the [ThirdPartyNotices.txt](./ThirdPartyNotices.txt) file for details regarding the licensing of Google Test.

# Supported features
GSL implements the following utilities:

Feature                            | Supported? | Description
-----------------------------------|:----------:|-------------
[**1. Views**][cg-views]           |            |
owner                              | ☑   | an alias for a raw pointer for its better expressiveness
not_null                           | ☑   | restricts a pointer / smart pointer to hold non-null values
strict_not_null                    | ☑   | a stricter version of `not_null` with explicit constructors
span                               | ☑   | spans a range starting from a pointer to pointer + size
span_p                             | ☐   | spans a range starting from a pointer to the first place for which the predicate is true
multi_span                         | ☑   | spans a contiguous region of memory, which represents a multidimensional array
strided_span                       | ☑   | **I HAVE NO IDEA WHAT IT DOES, ANYONE???!!!**
basic_zstring                      | ☑   | a pointer to a C-string (zero-terminated array) with a templated char type
zstring                            | ☑   | an alias to `basic_zstring` where the char type is char
wzstring                           | ☑   | an alias to `basic_zstring` where the char type is wchar_t
czstring                           | ☑   | like `zstring` but the char type is also const
cwzstring                          | ☑   | like `wzstring` but the char type is also const
u16zstring                         | ☑   | an alias to `basic_zstring` where the char type is char16_t
cu16zstring                        | ☑   | like `u16zstring` but the char type is also const
u32zstring                         | ☑   | an alias to `basic_zstring` where the char type is char32_t
cu32zstring                        | ☑   | like `u32zstring` but the char type is also const
basic_string_span                  | ☑   | like `span` but for strings with a templated string type
string_span                        | ☑   | an alias to `basic_string_span` where the char type is char
cstring_span                       | ☑   | like `string_span` but the char type is also const
wstring_span                       | ☑   | an alias to `basic_string_span` where the char type is wchar_t
cwstring_span                      | ☑   | like `wstring_span` but the char type is also const
u16string_span                     | ☑   | an alias to `basic_string_span` where the char type is char16_t
cu16string_span                    | ☑   | like `u16string_span` but the char type is also const
u32string_span                     | ☑   | an alias to `basic_string_span` where the char type is char32_t
cu32string_span                    | ☑   | like `u32string_span` but the char type is also const
[**2. Owners**][cg-owners]         |            |
unique_ptr                         | ☑   | an alias to `std::unique_ptr`
shared_ptr                         | ☑   | an alias to `std::shared_ptr`
stack_array                        | ☐   | a stack-allocated array
dyn_array                          | ☐   | a heap-allocated array
[**3. Assertions**][cg-assertions] |            |
Expects                            | ☑   | a precondition assertion; on failure it either terminates or throws `fail_fast`
Ensures                            | ☑   | a postcondition assertion; on failure it either terminates or throws `fail_fast`
[**4. Utitilies**][cg-utilities]   |            |
move_owner                         | ☐   | a helper function that moves one `owner` to the other
release_owner                      | ☐   | a helper function that releases ownership of the passed `owner` and returns a new `owner`
byte                               | ☑   | either an alias to std::byte or a byte type
fail_fast                          | ☑   | a custom exception type thrown by assertions
final_action                       | ☑   | a RAII style class that invokes a functor on its destruction
finally                            | ☑   | a helper function instantiating `final_action`
GSL_SUPPRESS                       | ☑   | a macro that takes an argument and tries to turn it into `[[gsl::suppress(x)]]`
[[implicit]]                       | ☐   | a "marker" to put on single-argument constructors to explicitly make them non-explicit
index                              | ☑   | a type to use for all container and array indexing (currently an alias for std::ptrdiff_t)
joining_thread                     | ☐   | a RAII style version of `std::thread` that joins
narrow                             | ☑   | a checked version of narrow_cast; it can throw `narrowing_error`
narrow_cast                        | ☑   | a narrowing cast for values and a synonym for static_cast
narrowing_error                    | ☑   | a custom exception type thrown by `narrow()`
[**5. Concepts**][cg-concepts]     | ☐   |

This is based on [CppCoreGuidelines semi-specification](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gsl-guidelines-support-library).

[cg-views]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslview-views
[cg-owners]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslowner-ownership-pointers
[cg-assertions]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslassert-assertions
[cg-utilities]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslutil-utilities
[cg-concepts]: https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#gslconcept-concepts

# Quick Start
## Supported Compilers
The GSL officially supports the current and previous major release of MSVC, GCC, Clang, and XCode's Apple-Clang.
See our latest test results for the most up-to-date list of supported configurations.

Compiler |Toolset Versions Currently Tested| Build Status
:------- |:--|------------:
 XCode |11.4 & 10.3 | [![Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL)
 GCC |9 & 8| [![Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL)
 Clang |11 &  10| [![Status](https://travis-ci.org/Microsoft/GSL.svg?branch=master)](https://travis-ci.org/Microsoft/GSL)
 Visual Studio with MSVC | VS2017 (15.9) & VS2019 (16.4) | [![Status](https://ci.appveyor.com/api/projects/status/github/Microsoft/GSL?svg=true)](https://ci.appveyor.com/project/neilmacintosh/GSL)
 Visual Studio with LLVM | VS2017 (Clang 9) & VS2019 (Clang 10) | [![Status](https://ci.appveyor.com/api/projects/status/github/Microsoft/GSL?svg=true)](https://ci.appveyor.com/project/neilmacintosh/GSL)


Note: For `gsl::byte` to work correctly with Clang and GCC you might have to use the ` -fno-strict-aliasing` compiler option.

---
If you successfully port GSL to another platform, we would love to hear from you!
- Submit an issue specifying the platform and target.
- Consider contributing your changes by filing a pull request with any necessary changes.
- If at all possible, add a CI/CD step and add the button to the table below!

Target | CI/CD Status
:------- | -----------:
iOS | ![CI](https://github.com/microsoft/GSL/workflows/CI/badge.svg)
Android | ![CI](https://github.com/microsoft/GSL/workflows/CI/badge.svg)

Note: These CI/CD steps are run with each pull request, however failures in them are non-blocking.

## Building the tests
To build the tests, you will require the following:

* [CMake](http://cmake.org), version 3.1.3 (3.2.3 for AppleClang) or later to be installed and in your PATH.

These steps assume the source code of this repository has been cloned into a directory named `c:\GSL`.

1. Create a directory to contain the build outputs for a particular architecture (we name it c:\GSL\build-x86 in this example).

        cd GSL
        md build-x86
        cd build-x86

2. Configure CMake to use the compiler of your choice (you can see a list by running `cmake --help`).

        cmake -G "Visual Studio 15 2017" c:\GSL

3. Build the test suite (in this case, in the Debug configuration, Release is another good choice).

        cmake --build . --config Debug

4. Run the test suite.

        ctest -C Debug

All tests should pass - indicating your platform is fully supported and you are ready to use the GSL types!

## Building GSL - Using vcpkg

You can download and install GSL using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:

    git clone https://github.com/Microsoft/vcpkg.git
    cd vcpkg
    ./bootstrap-vcpkg.sh
    ./vcpkg integrate install
    vcpkg install ms-gsl

The GSL port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.

## Using the libraries
As the types are entirely implemented inline in headers, there are no linking requirements.

You can copy the [gsl](./include/gsl) directory into your source tree so it is available
to your compiler, then include the appropriate headers in your program.

Alternatively set your compiler's *include path* flag to point to the GSL development folder (`c:\GSL\include` in the example above) or installation folder (after running the install). Eg.

MSVC++

    /I c:\GSL\include

GCC/clang

    -I$HOME/dev/GSL/include

Include the library using:

    #include <gsl/gsl>

## Usage in CMake

The library provides a Config file for CMake, once installed it can be found via

    find_package(Microsoft.GSL CONFIG)

Which, when successful, will add library target called `Microsoft.GSL::GSL` which you can use via the usual
`target_link_libraries` mechanism.

## Debugging visualization support
For Visual Studio users, the file [GSL.natvis](./GSL.natvis) in the root directory of the repository can be added to your project if you would like more helpful visualization of GSL types in the Visual Studio debugger than would be offered by default.