This document specifies how to contribute code to this repository.

Git Workflow

CAF's git workflow encompasses the following key aspects. (For general git style guidelines, see https://github.com/agis-/git-style-guide.)

The master branch always reflects a production-ready state, i.e., the latest release version.
The develop branch is the main development branch. A maintainer merges into master for a new release when it reaches a stable point. The develop branch reflects the latest state of development and should always compile.
Simple bugfixes consisting of a single commit can be pushed to develop.
Fixes for critical issues can be pushed to master (and develop) after talking to a maintainer (and then cause a new release immediately).
For new features and non-trivial fixes, CAF uses topic branches which branch off develop with a naming convention of topic/short-description. After completing work in a topic branch, check the following steps to prepare for a merge back into develop:
- Squash your commits into a single one if necessary
- Create a pull request to develop on github
- Wait for the results of Jenkins and fix any reported issues
- Ask a maintainer to review your work after Jenkins greelights your changes
- Address the feedback articulated during the review
- A maintainer will merge the topic branch into develop after it passes the code review

Commit Message Style

The first line succintly summarizes the changes in no more than 50 characters. It is capitalized and written in and imperative present tense: e.g., "Fix bug" as opposed to "Fixes bug" or "Fixed bug".
The first line does not contain a dot at the end. (Think of it as the header of the following description).
The second line is empty.
Optional long descriptions as full sentences begin on the third line, indented at 72 characters per line.

Coding Style

When contributing source code, please adhere to the following coding style, whwich is loosely based on the Google C++ Style Guide and the coding conventions used by the C++ Standard Library.

Example for the Impatient

// libcaf_example/caf/example/my_class.hpp

#ifndef CAF_EXAMPLE_MY_CLASS_HPP
#define CAF_EXAMPLE_MY_CLASS_HPP

#include <string>

// use "//" for regular comments and "///" for doxygen

namespace caf {
namespace example {

/// This class is only being used as style guide example.
class my_class {
public:
  /// Brief description. More description. Note that CAF uses the
  /// "JavaDoc-style" autobrief option, i.e., everything up until the
  /// first dot is the brief description.
  my_class();

  /// Destructs `my_class`. Please use Markdown in comments.
  ~my_class();

  // suppress redundant @return if you start the brief description with "Returns"
  /// Returns the name of this instance.
  inline const std::string& name() const {
    return name_;
  }

  /// Sets the name of this instance.
  inline void name(const std::string& new_name) {
    name_ = new_name;
  }

  /// Prints the name to `STDIN`.
  void print_name() const;

  /// Does something (maybe).
  void do_something();

  /// Does something else.
  void do_something_else();

private:
  std::string name_;
};

} // namespace example
} // namespace caf

#endif // CAF_EXAMPLE_MY_CLASS_HPP

// libcaf_example/src/my_class.cpp

#include "caf/example/my_class.hpp"

#include <iostream>

namespace caf {
namespace example {

namespace {

constexpr const char default_name[] = "my object";

} // namespace <anonymous>

my_class::my_class() : name_(default_name) {
  // nop
}

my_class::~my_class() {
  // nop
}

void my_class::print_name() const {
  std::cout << name() << std::endl;
}

void my_class::do_something() {
  if (name() == default_name) {
    std::cout << "You didn't gave me a proper name, so I "
              << "refuse to do something."
              << std::endl;
  } else {
    std::cout << "You gave me the name " << name()
              << "... Do you really think I'm willing to do something "
                 "for you after insulting me like that?"
              << std::endl;
  }
}

void my_class::do_something_else() {
  switch (default_name[0]) {
    case 'a':
      // handle a
      break;
    case 'b':
      // handle b
      break;
    default:
      handle_default();
  }
}

} // namespace example
} // namespace caf

General

Use 2 spaces per indentation level.
The maximum number of characters per line is 80.
No tabs, ever.
Never use C-style casts.
Vertical whitespaces separate functions and are not used inside functions: use comments to document logical blocks.
Header filenames end in .hpp, implementation files end in .cpp.
Never declare more than one variable per line.
* and & bind to the type, e.g., const std::string& arg.
Namespaces and access modifiers (e.g., public) do not increase the indentation level.
In a class, use the order public, protected, and then private.
Always use auto to declare a variable unless you cannot initialize it immediately or if you actually want a type conversion. In the latter case, provide a comment why this conversion is necessary.
Never use unwrapped, manual resource management such as new and delete.
Never use typedef; always write using T = X in favor of typedef X T.
Keywords are always followed by a whitespace: if (...), template <...>, while (...), etc.
Leave a whitespace after ! to make negations easily recognizable:
```
if (! sunny())
  stay_home();
else 
  go_outside();
```
Opening braces belong to the same line:
```
void foo() {
  // ...
}
```

Use standard order for readability: C standard libraries, C++ standard libraries, other libraries, (your) CAF headers:

// some .hpp file

#include <sys/types.h>

#include <vector>

#include "3rd/party.h"

#include "caf/fwd.hpp"

CAF includes should always be in doublequotes, whereas system-wide includes in angle brackets. In a .cpp file, the implemented header always comes first and the header caf/config.hpp can be included second if you need platform-dependent headers:

// example.cpp

#include "caf/example.hpp" // header related to this .cpp file

#include "caf/config.hpp"

#ifdef CAF_WINDOWS
#include <windows.h>
#else
#include <sys/socket.h>
#endif

#include <algorithm>

#include "some/other/library.h"

#include "caf/actor.hpp"

When declaring a function, the order of parameters is: outputs, then inputs. This follows the parameter order from the STL.
Protect single-argument constructors with explicit to avoid implicit conversions.

Naming

All names except macros and template parameters should be lower case and delimited by underscores.
Template parameter names should be written in CamelCase.
Types and variables should be nouns, while functions performing an action should be "command" verbs. Classes used to implement metaprogramming functions also should use verbs, e.g., remove_const.

Private and protected member variables use the suffix _ while getter and setter functions use the name without suffix:

class person {
public:
  const std::string& name() const {
    return name_
  }

  void name(const std::string& new_name) {
    name_ = new_name;
  }

private:
  std::string name_;
};

Use T for generic, unconstrained template parameters and x for generic function arguments. Suffix both with s for template parameter packs:
```
template <class... Ts>
void print(const Ts&... xs) {
  // ...
}
```

Headers

Each .cpp file has an associated .hpp file. Exceptions to this rule are unit tests and main.cpp files.
Each class has its own pair of header and implementation files and the relative path for the header file is derived from its full name. For example, the header file for caf::example::my_class of libcaf_example is located at libcaf_example/caf/example/my_class.hpp and the source file at libcaf_example/src/my_class.cpp.
All header files should use #define guards to prevent multiple inclusion. The symbol name is <RELATIVE>_<PATH>_<TO>_<FILE>_HPP.
Do not #include when a forward declaration suffices.
Each library component must provide a fwd.hpp header providing forward declartations for all types used in the user API.
Each library component must provide an all.hpp header that contains the main page for the documentation and includes all headers for the user API.
Use inline for small functions (rule of thumb: 10 lines or less).

Breaking Statements

Break constructor initializers after the comma, use four spaces for indentation, and place each initializer on its own line (unless you don't need to break at all):

my_class::my_class()
    : my_base_class(some_function()),
      greeting_("Hello there! This is my_class!"),
      some_bool_flag_(false) {
  // ok
}
other_class::other_class() : name_("tommy"), buddy_("michael") {
  // ok
}

Break function arguments after the comma for both declaration and invocation:

intptr_t channel::compare(const abstract_channel* lhs,
                          const abstract_channel* rhs) {
  // ...
}

Break before tenary operators and before binary operators:

if (today_is_a_sunny_day()
    && it_is_not_too_hot_to_go_swimming()) {
  // ...
}

Template Metaprogramming

Despite its power, template metaprogramming came to the language pretty much by accident. Templates were never meant to be used for compile-time algorithms and type transformations. This is why C++ punishes metaprogramming with an insane amount of syntax noise. In CAF, we make excessive use of templates. To keep the code readable despite all the syntax noise, we have some extra rules for formatting metaprogramming code.

Brake using name = ... statements always directly after = if it does not fit in one line.
Consider the semantics of a metaprogramming function. For example, std::conditional is an if-then-else construct. Hence, place the if-clause on its own line and do the same for the two cases.

Use one level of indentation per "open" template and place the closing >, >::type or >::value on its own line. For example:

using optional_result_type =
  typename std::conditional<
    std::is_same<result_type, void>::value,
    bool,
    optional<result_type>
  >::type;
// think of it as the following (not valid C++):
auto optional_result_type =
  conditional {
    if   result_type == void
    then bool
    else optional<result_type>
  };

Note that this is not necessary when simply defining a type alias. When dealing with "ordinary" templates, indenting based on the position of the opening < is ok, e.g.:
```
using response_handle_type = response_handle<Subtype, message,
                                             ResponseHandleTag>;
```

Preprocessor Macros

Use macros if and only if you can't get the same result by using inline functions or proper constants.
Macro names use the form CAF_<COMPONENT>_<NAME>.

Comments

Doxygen comments start with ///.
Use Markdown instead of Doxygen formatters.
Use @cmd rather than \cmd.
Use // to define basic comments that should not be swallowed by Doxygen.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

CONTRIBUTING.md

CONTRIBUTING.md

Git Workflow

Commit Message Style

Coding Style

Example for the Impatient

General

Naming

Headers

Breaking Statements

Template Metaprogramming

Preprocessor Macros

Comments

Files

CONTRIBUTING.md

Latest commit

History

CONTRIBUTING.md

File metadata and controls

Git Workflow

Commit Message Style

Coding Style

Example for the Impatient

General

Naming

Headers

Breaking Statements

Template Metaprogramming

Preprocessor Macros

Comments