Packages: The Building Blocks of C++ Development

In the ever-evolving world of C++, managing code effectively is paramount. Packages, a fundamental concept in software distribution, provide a structured approach to organizing and distributing reusable components. This blog post delves into the core elements of C++ packages, their essential properties, and how they streamline the development process and proposes a set of core concepts that should be captured by any specification.

The reason this is so important from a CI design point of view is creating an effective caching solution to help improve build times. Avoid uploading unnecessary files is an imperative requirement for this strategy.

Unpacking the Essentials: What Makes a C++ Package

A C++ package encapsulates a collection of core artifacts, the lifeblood of your codebase. This does not extend to delivering the product for example as on-premise software but might be bundled for a software development kit. These artifacts serve as building blocks that are ingested by build systems to execute the compilation, archiving, and linking processes. Here's a breakdown of the key components:

• Core Artifacts:
  • Headers (.hpp files): These files contain declarations (functions, classes, variables, etc.) that serve as blueprints for your code. Other source files can #include headers to access the declared entities.
  • Libraries (Static and Shared): These are compiled archives (.a or .lib for static, .so or .dll for shared) that bundle object code representing compiled functions and variables. Libraries provide reusable functionality that can be integrated into your programs.
  • Binary Modules (C++20 Modules): C++20 introduces modules (.ixx files) as a more granular unit of code organization and compilation compared to traditional headers. They enable stricter dependency management and improve build times.
• Supporting Artifacts:
  • License Information (.txt or .md files): It's crucial to include licensing details to comply with copyright and distribution requirements.

There's often a temptation to include Executables (.exe or .out); these can be utilities used during the build process, such as code generators or testing frameworks. However I'd argue there's likely an extension to the idea of a "package" called "tool" which could be specialized and more adapt at covering this use case.

The Package Imperative: What Makes a Valid Package?

To guarantee robust development, C++ packages must adhere to specific criteria:

• One Definition Rule (ODR) Compliance: Package contents must strictly follow the ODR, ensuring there's only one definition for a given entity across all included files. This prevents ambiguities and potential compilation errors.
• Well-Formed Programs: A valid package must yield functional, well-formed programs when all its core artifacts are consumed. Errors arising from improper interaction between different components disqualify a package.

The primary goal is to enable downstream consumption; capturing the inputs for the compiler is the practical application of this concept. Packages should be readily consumable by other build systems for downstream projects. A clear and well-defined interface is essential for smooth integration.

Beyond the Bare Essentials: Configuration Considerations

While core artifacts form the foundation of a package, however there is more information necessary for compiling and linking which plays a vital role in specifying details like:

• Compiler Flags: These flags control the behavior of the compiler, influencing optimization levels, warning modes, and other compilation settings.
• Include Paths: Build systems need to know where to locate headers during the compilation process. Package specifications should explicitly define include paths to avoid errors.
• Linker Flags: Linker flags instruct the linker on how to combine object files (libraries) into executable programs. These can be specified within package configurations.
• Library and Library Path: Packages may depend on external libraries. Explicitly declaring required libraries and their paths facilitates linking during the build.

Avoid Binary Compatibility

C++ packages benefit from avoiding binary compatibility information within the package itself. This simplifies package and leaves the that be tooling specific; often teams have contradictory requirements (save it or break it) and the tooling or vendor specific implementation should not be decided here.

The Build System Should not Care:

• Build systems like CMake or Make are adept at handling platform-specific configurations. They take compiler flags, target architectures, and other factors into account to ensure correct compilation and linking.

Package Managers, Right Tool for the Job:

• Package managers like Conan or vcpkg offer a powerful solution for dependency management.
• They maintain a database of packages with specific versions and configurations (triplets) catering to different environments.
• When a new project depends on a package, the package manager can:
  1. Rebuild from source if the package has no compatibility information, ensuring the build process leverages the specific project's configuration.
  2. Strict Compatibility Checks (for packages with well-defined compatibility):
     • The package manager verifies if the existing package version aligns with the project's requirements.
     • If so, the package can be reused, saving build time.
     • If not, the manager triggers a rebuild from source.

The Case for "No Compatibility" Definition:

• By leaving binary compatibility out of the package metadata, the package becomes more adaptable.
• Build systems and package managers can then apply their knowledge and strategies for optimal builds.
• This reduces duplication of effort and streamlines the development process.

Trade-offs and Best Practices:

• While avoiding binary compatibility information generally simplifies package management, there are situations where pre-built binaries might be beneficial (e.g., for performance optimization on a specific system).
• In such cases, package managers often offer mechanisms for providing pre-built binaries with clear versioning and compatibility guidelines.

However, as a general rule, keeping packages free of binary compatibility information promotes flexibility and maintainability for C++ projects in diverse environments. This approach fosters collaboration between packages, builds systems, and package managers, resulting in more robust and adaptable C++ development ecosystems.

Conclusion: Packages - The Powerhouse of C++ Development

Packages empower C++ developers with a structured and efficient way to organize code, promote reusability, and ensure project maintainability. By adhering to the essential properties outlined in this guide, you can craft robust and portable packages that act as the cornerstones of successful C++ development endeavors.

Ready to Dive Deeper?

For further exploration, consider delving into specific build systems like CMake or Make to understand how they handle package creation and configuration. Explore popular package managers like Conan or vcpkg that simplify dependency management and facilitate the sharing of C++ packages across diverse projects.