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For low-level styling (spaces, parentheses, brace placement, etc), all code should follow the format specified in .clang-format in the project root.
Important: Make sure you use the correct version of clang-format!See lint-clang-format.py for the version enforced in CI.See AdvancedBuildInstructions.md for instructions on how to get an up-to-date version if your OS distribution does not ship the correct version.
This document describes the coding style used for C++ code in the Ladybird Browser project. All new code should conform to this style. We’ll definitely be tweaking and amending this over time, so let’s consider it a living document. :)

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Names

A combination of CamelCase, snake_case, and SCREAMING_CASE:
  • Use CamelCase (Capitalize the first letter, including all letters in an acronym) in a class, struct, or namespace name
  • Use snake_case (all lowercase, with underscores separating words) for variable and function names
  • Use SCREAMING_CASE for constants (both global and static member variables)
struct Entry;
size_t buffer_size;
class FileDescriptor;
String absolute_path();

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Wrong

struct data;
size_t bufferSize;
class Filedescriptor;
String MIME_Type();

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Matching spec naming

When implementing spec algorithms and other constructs that a spec explicitly names, prefer closely matching the same names the spec uses, whenever possible. Given the construct at https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#suffering-from-being-missing which has the literal name “Suffering from being missing” in the spec, for example: 
bool HTMLInputElement::suffering_from_being_missing(); // exactly matches the spec naming

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Full words vs abbreviations

Use full words, except in the rare case where an abbreviation would be more canonical and easier to understand. 
size_t character_size;
size_t length;
short tab_index; // More canonical.

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Data members

Data members in C++ classes should be private. Static data members should be prefixed by “s_”. Other data members should be prefixed by “m_”. Global variables should be prefixed by “g_”. 
class String {
public:
    ...

private:
    int m_length { 0 };
};

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Setters and getters

Precede setters with the word “set”. Use bare words for getters. Setter and getter names should match the names of the variables being set/gotten. 
void set_count(int); // Sets m_count.
int count() const; // Returns m_count.
Precede getters that return values through out arguments with the word “get”. 
void get_filename_and_inode_id(String&, InodeIdentifier&) const;

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Function names

Use descriptive verbs in function names. 
bool convert_to_ascii(short*, size_t);

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The ensure_ prefix

When there are two getters for a variable, and one of them automatically makes sure the requested object is instantiated, prefix that getter function with ensure_. As it ensures that an object is created, it should consequently also return a reference, not a pointer. 
Inode* inode();
Inode& ensure_inode();

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Function parameters

Leave meaningless variable names out of function declarations. A good rule of thumb is if the parameter type name contains the parameter name (without trailing numbers or pluralization), then the parameter name isn’t needed. Usually, there should be a parameter name for bools, strings, and numerical types. 
void set_count(int);
void do_something(Context*);

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Enums vs bools

Prefer enums to bools on function parameters if callers are likely to be passing constants, since named constants are easier to read at the call site. An exception to this rule is a setter function, where the name of the function already makes clear what the boolean is. 
do_something(something, AllowFooBar::Yes);
paint_text_with_shadows(context, ..., text_stroke_width > 0, is_horizontal());
set_resizable(false);

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Enum members

Enum members should use InterCaps with an initial capital letter.

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Header guards

Use #pragma once instead of #define and #ifdef for header guards. 
// MyClass.h
#pragma once

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Other punctuation

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Constructor initialization

Constructors for C++ classes should initialize their members using C++ initializer syntax. Each member (and superclass) should be indented on a separate line, with the colon or comma preceding the member on that line. Prefer initialization at member definition whenever possible. 
class MyClass {
    ...
    Document* m_document { nullptr };
    int m_my_member { 0 };
};

MyClass::MyClass(Document* document)
    : MySuperClass()
    , m_document(document)
{
}

MyOtherClass::MyOtherClass()
    : MySuperClass()
{
}

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Vector iterations

Prefer index or range-for over iterators in Vector iterations for terse, easier-to-read code. 
for (auto& child : children)
    child->do_child_thing();

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Pointers and references

Both pointer types and reference types should be written with no space between the type name and the * or &. An out argument of a function should be passed by reference except rare cases where it is optional in which case it should be passed by pointer. 
void MyClass::get_some_value(OutArgumentType& out_argument) const
{
    out_argument = m_value;
}

void MyClass::do_something(OutArgumentType* out_argument) const
{
    do_the_thing();
    if (out_argument)
        *out_argument = m_value;
}

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”using” statements

In header files in the AK sub-library, however, it is acceptable to use “using” declarations at the end of the file to import one or more names in the AK namespace into the global scope. 
// AK/Vector.h

namespace AK {

} // namespace AK

using AK::Vector;
In C++ implementation files, do not use “using” declarations of any kind to import names in the standard template library. Directly qualify the names at the point they’re used instead. 
// File.cpp

std::swap(a, b);
c = std::numeric_limits<int>::max()

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Types

Omit “int” when using “unsigned” modifier. Do not use “signed” modifier. Use “int” by itself instead. 
unsigned a;
int b;

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Classes

For types with methods, prefer class over struct.
  • For classes, make public getters and setters, keep members private with m_ prefix.
  • For structs, let everything be public and skip the m_ prefix.
struct Thingy {
    String name;
    int frob_count { 0 };
};

class Doohickey {
public:
    String const& name() const { return m_name; }
    int frob_count() const { return m_frob_count; }

    void jam();

private:
    String m_name;
    int m_frob_count { 0 };
}

​
Implicit conversions

Use a constructor to do an implicit conversion when the argument is reasonably thought of as a type conversion and the type conversion is fast. Otherwise, use the explicit keyword or a function returning the type. This only applies to single argument constructors. 
class LargeInt {
public:
    LargeInt(int);
...

class Vector {
public:
    explicit Vector(int size); // Not a type conversion.
    Vector create(Array); // Costly conversion.
...

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Singleton pattern

Use a static member function named “the()” to access the instance of the singleton. 
class UniqueObject {
public:
    static UniqueObject& the();
...

​
Comments

Comments should be written using // and not /* */, except for the copyright notice. Write comments as proper sentences starting with a capital letter and ending with a period (or other punctuation). One exception may be end of line comments like this: if (x == y) // false for NaN Another exception is comments copied from specifications. These should be quoted verbatim, and not modified except for wrapping or to insert necessary punctuation such as adding ** when a number is raised to a power, as this is often done using elements like <sup> which do not appear in the copied text. Please wrap long comments onto multiple lines so that they are easier to read. Generally, 120 characters is a good width to aim for. Use FIXME: (without attribution) to denote items that need to be addressed in the future. TODO: (without attribution) is also permitted. 
draw_jpg(); // FIXME: Make this code handle jpg in addition to the png support.
Explain why the code does something. The code itself should already say what is happening. 
i++; // Go to the next page.

// Let users toggle the advice functionality by clicking on catdog.
catdog_widget.on_click = [&] {
    if (advice_timer->is_active())
        advice_timer->stop();
    else
        advice_timer->start();
};

​
Spec notes

Many web specs include notes that are prefixed with NOTE: .... To allow for verbatim copying of these notes into our code, we retain the NOTE: prefix and use NB: for our own notes. This only applies to comments as part of code that is directly implementing a spec algorithm or behavior. Comments in other places do not need a prefix. 
// 2. If property is in already serialized, continue with the steps labeled declaration loop.
// NOTE: The prefabulated aluminite will not be suitable for use here. If the listed spec note is so long that we reach
//       column 120, we wrap around and indent the lines to match up with the first line.
// NB: We _can_ actually use the aluminite since we unprefabulated it in step 1 for performance reasons.

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Overriding virtual methods

The declaration of a virtual method inside a class must be declared with the virtual keyword. All subclasses of that class must also specify either the override keyword when overriding the virtual method, or the final keyword when overriding the virtual method and requiring that no further subclasses can override it. 
class Person {
public:
    virtual String description() { ... };
}

class Student : public Person {
public:
    virtual String description() override { ... }; // This is correct because it contains both the "virtual" and "override" keywords to indicate that the method is overridden.
}

class Person {
public:
    virtual String description() { ... };
}

class Student : public Person {
public:
    virtual String description() final { ... }; // This is correct because it contains both the "virtual" and "final" keywords to indicate that the method is overridden and that no subclasses of "Student" can override "description".
}

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Const placement

Use “east const” style where const is written on the right side of the type being qualified. See this article for more information about east const. 
Salt const& m_salt;

​
Casts

Before you consider a cast, please see if your problem can be solved another way that avoids the visual clutter.
  • Integer constants can be specified to have (some) specific sizes with postfixes like u, l, ul etc. The same goes for single-precision floating-point constants with f.
  • Working with smaller-size integers in arithmetic expressions is hard because of implicit promotion. Generally, it is fine to use int and other “large” types in local variables, and possibly cast at the end.
  • If you const_cast, really consider whether your APIs need to be adjusted in terms of their constness. Does the member function you’re writing actually make sense to be const?
  • If you do checked casts between base and derived types, also consider your APIs. For example: Does the function being called actually need to receive the more general type or is it fine with the more specialized type?
If you do need to cast: Don’t use C-style casts. The C-style cast has complex behavior that is undesired in many instances. Be aware of what sort of type conversion the code is trying to achieve, and use the appropriate (!) C++ cast operator, like static_cast, reinterpret_cast, bit_cast, dynamic_cast etc. There is a single exception to this rule: marking a function parameter as used with (void)parameter;. 
MyParentClass& object = get_object();
// Verify the type...
MyChildClass& casted = static_cast<MyChildClass&>(object);

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Omission of curly braces from statement blocks

Curly braces may only be omitted from if/else/for/while/etc. statement blocks if the body is a single line. Additionally, if any body of a connected if/else statement requires curly braces according to this rule, all of them do. 
if (condition)
    foo();

if (condition) {
    foo();
    bar();
}

if (condition) {
    foo();
} else if (condition) {
    bar();
    baz();
} else {
    qux();
}

for (size_t i = i; condition; ++i) {
    if (other_condition)
        foo();
}

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