🔗 Code style guidelines

details labeled ENFORCED are checked and forced by source testing mechanisms.

🔗 C++ Guidelines

• const-correctnes help

🔗 Source formatting guidelines

• We have an astyle wrapper that formats the code without breaking it.
• If you have astyle version 3.1 please format your changes with ~/scripts/formater.pl
• This formatter is run regularly over the entire code to enforce certain guidelines but it helps reduce trouble if your code matches those guidelines when submitted.

🔗 ENFORCED rules

• 4-space indentation, no tabs
• no trailing whitespace on any line
• no sets of multiple empty lines. One is enough to separate things.
• one space between if and its parameter () brackets
• construct open braces { begin on the same line as their construct (if, while)
• within a conditional, assignment must be surrounded with ( braces: if ((a = b))... but a local variable declaration and initialization must not be: if (T a = b)....

The formater is known to enforce some weird indentation at times. Notably after #if ... #endif directives. If you find these, please ignore for now. They will be corrected in a later version of the formater.

🔗 Mandatory coding rules

• Document, at least briefly, every new type, class, member, or global. Doxygen format is appreciated.
• The Big Five (Three plus Two)
  • Big Three: copy constructor, destructor, and assignment operator
  • Move methods: move constructor and move assignment operator
    1. If the class works well without any of the Big3 methods, do not define any of the Big3 methods.
    2. If you have to define one of Big3, declare all of Big3.
    3. If class has a non-default destructor, you may decide to define one of the Move methods. If you define one Move method, declare the other Move method as well.
    4. use = default declaration whenever possible if it is sufficient and = delete declaration when method is prohibited.
• Avoid adding new globals as detailed in the section below.
• Naming conventions as covered in Features/SourceLayout are to be used.

🔗 Rule: No new globals

C++ globals are prone to several initialization order-related problems. In most cases, globals are unnecessary. Unnecessary globals should not be added to Squid. In most cases, an unnecessary global Foo of type Type should be replaced with the following wrapper function:

auto &
Foo()
{
    static const auto foo = new Type(...);
    return *foo;
}

The function may be marked static, become a class member, adjusted to return a constant reference, and/or contain more complex object initialization code, as needed.

The increased performance cost of accessing an object through a function wrapper (as opposed to direct access to a global object) is not a valid excuse for avoiding a global.

This rule applies to all new objects that are (or may become) susceptible to initialization order problems, including globals in the global namespace, namespace-scope globals, and class-scope static members (regardless of their access modifiers). This rule does not apply to function-scoped variables.

This rule does apply to would-be globals of built-in/intrinsic types because they may be subject to similar initialization problems.

This rule does not apply to existing globals. The global prior existence is determined by its name. For example, changing the type of an existing global does not automatically subject that global to this rule, especially if many users of that global remain unchanged. A dedicated pull request may propose to convert an existing global if the authors think that the benefits of the conversion outweigh its negative side effects, of course.

To avoid deinitialization order problems, the wrapper function must dynamically allocate the would-be global to prevent its destruction. In very rare cases where the global must be destructed at the end of the program, a Nifty Counter may be used instead of the wrapper function.

🔗 Suggested coding rules

• Use internally consistent naming scheme (see below for choices).
• Words in global names and all type names are CamelCase capitalized:
  • including the first word.
  • acronyms are to be downcased to fit (ie Http)
  • This includes namespaces, class types, global variables, static class members, and macros
• Use const qualifiers in declarations as much as appropriate
• Use bool for boolean types
• Avoid macros
• Do not start names with an underscore
• Do not end a member name with underscore. Unless the name collides with a method name
• Use prefix form for increment and decrement operators (i.e. ++c instead of c++)
• When a method is inherited and overloaded locally it should be grouped under a one-line comment naming the API where it comes from

🔗 Word capitalization example

namespace Foo // namespace name CamelCased
{

class ClassStats; // class type name CamelCased

class ClassName
{
public:
  static ClassStats &Stats(); // static methods use CameCased

  void clear();

private:
  static ClassStats Stats_; // static member CamelCased. Underscore since name collides with Stats() method

  int internalState;
};

extern void ReportUsage(ostream &); // global function CamelCased

🔗 Class declaration layout

class Foo : public Bar
{
  CBDATA_* or MEMPROXY_* special macro.

public:
  all public typedef

  all constructors and operators
  Foo destructor (if any)

  /* Bar API */
  all methods overloaded from FooBar parent class

  all public static methods
  all public member methods

  all public static variables
  all public member variables

protected:
  all protected static methods
  all protected member methods

  all protected static variables
  all protected member variables

private:
  all private static methods
  all private member methods

  all private static variables
  all private member variables
};

🔗 Member naming

Pick one of the applicable styles described below and stick to it. For old classes, try to pick the style which is closer to the style being used.

1. Accessors

   Explicit set, get, has :

   void setMember(const Member &);
   const Member &getMember() const; // may also return a copy
   Member &getMember();
   bool hasMember() const;
   

   OR Compact:

   void member(const Member &);
   const Member &member() const; // may also return a copy
   Member &member();
   bool hasMember() const;
   

2. Data members

   For public data members, do not use underscore suffix. Use verb prefixes for boolean members.

    int counter;
    int next;
    bool isClean;
    bool sawHeader;
   

   For protected and private data members: May use underscore suffix to emphasize that the data member is not public and must use underscore suffix if the data member name would otherwise clash with a method name. Use verb prefixes for boolean members.

    int counter_;
    int next_;
    bool isClean_;
    bool sawHeader_;
   

3. State checks
   • prefixed with an appropriate verb: is, has/have, can

        bool canVerb() const;
        bool hasNoun() const;
        bool haveNoun() const; // if class name is plural
        bool isAdjective() const; // but see below
     

   • Avoid negative words because double negation in if-statements will be confusing; let the caller negate when needed.

        bool notAdjective() const; // XXX: avoid due to !notAdjective()
     

   • The verb is may be omitted, especially if the result cannot be confused with a command: the confusion happens if the adjective after is can be interpreted as a verb

      bool isAtEnd() const; // OK, but excessive
      bool atEnd() const; // OK, no confusion
   
      bool isFull() const;  // OK, but excessive
      bool full() const;  // OK, no confusion
   
      bool clear() const; // XXX: may look like a command to clear state
      bool empty() const; // XXX: may look like a "become empty" command
   

🔗 File #include guidelines

1. minimal system includes
2. custom headers provided by Squid:
   • place internal header includes above system includes
   • omit wrappers
   • always include with double-quotes (“”)
   • ENFORCED: sort alphabetically
   • use full path (only src/ prefix may be omitted)
3. system C++ headers (without any extension suffix):
   • always include with <>
   • omit any HAVE_ wrapper
   • sort alphabetically
   • if the file is not portable, do not use it
4. system C headers (with a .h suffix):
   • always include with <>
   • mandatory HAVE_FOO_H wrapper
   • avoid where C++ alternative is available
   • sort alphabetically
   • should import order-dependent headers through libcompat

ENFORCED

• sort internal includes alphabetically

.cc files only:

• include squid.h as their first include file.

.h and .cci files

• DO NOT include squid.h

Layout Example:

// local includes sorted alphabetically with squid.h first
#include "squid.h"
#include "comm/forward.h"
#include "local.h"

// system C++ includes alphabetically sorted and not-wrapped
#include <cstdlib>
#include <iostream>

// System C includes alphabetically sorted and wrapped
#if HAVE_ACCESS_H
#include <access.h>
#endif
#if HAVE_GETOPT_H
#include <getopt.h>
#endif

🔗 Component Macros in C++

Squid uses autoconf defined macros to eliminate experimental or optional components at build time.

• name in C++ code should start with USE_
• test with #if and #if ! rather than #ifdef or #ifndef
• should be wrapped around all code related solely to a component; including compiler directives and #include statements

ENFORCED:

• MUST be used inside .h to wrap relevant code.

🔗 See Also

• DeveloperResources.

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