Mesos C++ Style Guide

The Mesos codebase follows the Google C++ Style Guide with the following differences:

Naming

Variable Names

• We use lowerCamelCase for variable names (Google uses snake_case, and their class member variables have trailing underscores).

Constant Names

• We use lowerCamelCase for constant names (Google uses a k followed by mixed case, e.g. kDaysInAWeek).

Function Names

• We use lowerCamelCase for function names (Google uses mixed case for regular functions; and their accessors and mutators match the name of the variable).
• Leave spaces around overloaded operators, e.g. operator + (...); rather than operator+(...);

Namespace Names

• We do not use namespace aliases.

Strings

• Strings used in log and error messages should end without a period.

Comments

• End each sentence with a period.
• At most 70 characters per line in comments.
• For trailing comments, leave one space.

Breaks

• Break before braces on function, class, struct and union definitions. (Google attaches braces to the surrounding context)

Indentation

Class Format

• Access modifiers are not indented (Google uses one space indentation).
• Constructor initializers are indented by 2 spaces (Google indents by 4).

Function Definition/Invocation

• Newline when calling or defining a function: indent with 4 spaces.
• We do not follow Google's style of wrapping on the open parenthesis, the general goal is to reduce visual "jaggedness" in the code. Prefer (1), (4), (5), sometimes (3), never (2):

// 1: OK.
allocator->resourcesRecovered(frameworkId, slaveId, resources, filters);

// 2: Don't use.
allocator->resourcesRecovered(frameworkId, slaveId,
                           resources, filters);

// 3: Don't use in this case due to "jaggedness".
allocator->resourcesRecovered(frameworkId,
                              slaveId,
                              resources,
                              filters);

// 3: In this case, 3 is OK.
foobar(someArgument,
       someOtherArgument,
       theLastArgument);

// 4: OK.
allocator->resourcesRecovered(
    frameworkId,
    slaveId,
    resources,
    filters);

// 5: OK.
allocator->resourcesRecovered(
    frameworkId, slaveId, resources, filters);

Continuation

• Newline for an assignment statement: indent with 2 spaces.

Try<Duration> failoverTimeout =
  Duration::create(FrameworkInfo().failover_timeout());

Empty Lines

• 1 blank line at the end of the file.
• Elements outside classes (classes, structs, global functions, etc.) should be spaced apart by 2 blank lines.
• Elements inside classes (member variables and functions) should not be spaced apart by more than 1 blank line.

C++11

We still support older compilers. The whitelist of supported C++11 features is:

• Static assertions.
• Multiple right angle brackets.
• Type inference (auto and decltype). The main goal is to increase code readability. Here are several examples:

// 1: OK.
const auto& i = values.find(keys.front());
// Compare with
const typename map::iterator& i = values.find(keys.front());

// 2: Don't use.
auto authorizer = LocalAuthorizer::create(acls);
// Compare with
Try<Owned<LocalAuthorizer>> authorizer = LocalAuthorizer::create();

• Rvalue references.
• Variadic templates.
• Mutexes.
  • std::mutex.
  • std::lock_guard.
  • std::unique_lock.
• Shared from this.
  • class T : public std::enable_shared_from_this.
  • shared_from_this().