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Code standards

Formatting

clang-format is used to enforce most of the formatting rules, such as:

  • Tabs for indentation.
  • Open braces go on new lines.
  • Space before open parenthesis.
  • Space after comma.

Running ci/clang-format-all.sh on *nix systems is required before pushing your code to ensure that the formatting is good. If you want to do formatting from the IDE, chances are there's a plugin available. Visual studio for instance provides a way to automatically format on saving. The definition file .clang-format is located in the project root directory.

Make sure you set up your editor to use tabs. Use tabs for indentation, and spaces for alignment 1. That way, you can use any tab size you want in your favorite editor, but the code will still look good for people with different settings.

General guidelines

  • Use auto type inference for local variables if it's clear from the context what the type will be. Use your best judgement, sometimes adding explicit types can increase readability 2
  • Handle exceptions, including IO exceptions for file and network operations.
  • Be liberal with debug_assert. Use asserts to check invariants, not potential runtime errors, which should be handled gracefully. debug_assert has an advantage over normal assert as it will always print out the stacktrace of the current thread when it hits. Debug asserts are for detecting bugs, not error handling. There is also release_assert which is similar to debug_assert but also hits in a release build. When there is unexpected behaviour and no suitable way to recover it can be used to halt program execution.
  • Be liberal with logger.always_log or logger.try_log statements, except in performance critical paths.
  • Add comments to explain complex and subtle situations, but avoid comments that reiterates what the code already says.
  • Use RAII and C++11 smart pointers to manage memory and other resources.

Performance and scalabiliy considerations

  • When making changes, think about performance and scalability. Pick good data structures and think about algorithmic complexity.
    • For small data sets, std::vector should be your to-go container, as a linear scan through contiguous memory is often faster than any alternative due to memory being read in cache lines.
    • Nested loops yield quadratic behavior - is there an alternative? A typical example is removing an inner lookup loop with an unordered set/map to improve lookup performance to O(1).
  • Make sure your change doesn't conflict with the scalability characteristics described in the white paper.

Security

Your code will be reviewed with security in mind, but please do your part before creating a pull request:

  • Familiarize yourself with best practices for writing secure C++ code. In particular:

  • Use static and dynamic analysis tools, such as valgrind, XCode instrumentation, linters and sanitizers. These tools are also great for debugging crashes and performance problems.

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