Announcing Guidelines Support Library v4.2.0

GSL is an implementation of the Guidelines Support Library specified by the
C++ Core Guidelines.
It provides types and functions that help C++ developers write safer, more maintainable
code while following modern C++ best practices.

We are excited to announce the release of GSL v4.2.0! This release brings significant
performance improvements, new features, and important updates that align GSL with modern
C++ standards.

Performance Boost for Span Iterator

One of the most notable changes in this release is the significant performance
improvements of span_iterator when using the Clang compiler. Previously, gsl::span
iterators could be up to 20 times slower than std::span under various workloads
(range-for, <algorithm>, etc.). Through reorganization of the code and moving
access-checks out of the hot path, we have achieved performance parity for most
workloads (see #1168). This
ABI-preserving improvement makes gsl::span a more practical choice for code that is
both safe and fast.

New Features and Improvements

As the C++ Core Guidelines evolve with modern C++ practices, GSL continues to adapt and
grow. Working closely with the community, we’ve implemented key enhancements that make
GSL more robust and easier to use in modern C++ codebases. These updates focus on type
safety, modern idioms, and better template support — areas crucial for production
code. Here are some of the key improvements since version 4.1.0:

• GSL Swap Support: Introduced gsl::swap specifically designed for safely swapping
  gsl::not_null pointers
• Enhanced Type Traits: Added element_type to gsl::not_null<T> for better type
  trait consistency
• Improved Smart Pointer Support: Added support for strict_not_null with
  unique_ptr
• Better SFINAE: Improved template substitution behavior throughout the library

Alignment with C++ Standards

As part of our commitment to keeping GSL aligned with modern C++ development, we are
deprecating features that have been adopted into the C++ standard library. We recommend
using the C++ standard library equivalents for these features when possible. Here are
the features that have been deprecated in this release:

• gsl::unique_ptr
• gsl::shared_ptr
• gsl::byte (for C++17 and later)

Additionally, we have removed the long-deprecated string_span feature, encouraging
users to migrate to std::string_view.

Note: We continue to recommend using gsl::span as a safer alternative to
std::span.

Compatibility Updates

We want to make sure GSL runs well on the latest compilers and modern operating systems.
To that end, we have modernized our build infrastructure to validate that GSL is
supported by the latest development environments:

• Updated compiler support to include Clang 16 to 18 and GCC 12 to 14
• Upgraded to Ubuntu 24.04 in our CI pipeline

More information about our supported platforms can be found in our
README.

Bug Fixes and Standards Compliance

Several important bugs have been fixed in this release:

• Resolved a GCC-specific issue with list initialization of const references
• Fixed SFINAE implementation in gsl::owner
• Improved include directive handling to prevent conflicts with standard library headers
• Updated include paths to comply with C++ Core Guidelines

Try It Out

To start using GSL v4.2.0, you can either:

1. Install via vcpkg: vcpkg install ms-gsl
2. Download from GitHub:
   microsoft/GSL

For detailed release notes and migration guidance, please visit our
GitHub repository.

Contributing to GSL

This release would not have been possible without our community contributors. Special
thanks to the following individuals for their valuable contributions:

• @ajtruckle
• @apenn-msft
• @asartori86
• @beinhaerter
• @daltairwalter
• @DanielJump
• @HenryHu
• @lord-pando
• @mhthies
• @paparodeo
• @tiagomacarios

If you wish to contribute to GSL, please refer to our open issues and pull requests in
the Microsoft/GSL repository on GitHub. We welcome
your feedback and contributions!

Please remember to follow our
Code of Conduct when contributing to
GSL.

Feedback

In addition to contributing, we would love to hear your thoughts on the latest updates
to GSL! Please share your feedback and suggestions in the comments below.

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