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AK (short for “Agner’s Kit”) is Ladybird’s custom standard library that provides fundamental data structures, smart pointers, string types, and utility classes. Every component in Ladybird depends on AK for basic functionality.

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Core containers

AK provides efficient, modern C++ containers designed for browser development.

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Vector

Vector<T> is a dynamic array similar to std::vector but with Ladybird-specific optimizations: 
Vector<String> items;
items.append("Hello"_string);
items.append("World"_string);

for (auto const& item : items) {
    dbgln("Item: {}", item);
}
Key methods:
  • append() - Add element to end
  • prepend() - Add element to beginning
  • insert() - Insert at specific index
  • remove() - Remove by index
  • find() - Search for element
  • size() - Get element count

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HashMap

HashMap<K, V> provides hash-based key-value storage: 
HashMap<String, int> scores;
scores.set("Alice"_string, 100);
scores.set("Bob"_string, 95);

if (auto score = scores.get("Alice"_string); score.has_value()) {
    dbgln("Alice's score: {}", *score);
}

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Other containers

HashTable

Hash-based set for unique values

Optional

Type-safe nullable value wrapper

Variant

Type-safe union holding one of several types

Span

Non-owning view over contiguous data

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Smart pointers

AK includes three main smart pointer types for memory safety.

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OwnPtr and NonnullOwnPtr

Single-owner pointers for exclusive ownership: 
// Create using make<T>()
NonnullOwnPtr<MyClass> obj = make<MyClass>(arg1, arg2);

// For fallible allocation
auto obj_or_error = try_make<MyClass>();
if (obj_or_error.is_error()) {
    // Handle allocation failure
}
NonnullOwnPtr cannot be null, making it perfect for return types and parameters where null is invalid. It’s equivalent to passing by reference (&) but with ownership transfer.

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RefPtr and NonnullRefPtr

Reference-counted pointers for shared ownership: 
class MyObject : public RefCounted<MyObject> {
    // ...
};

NonnullRefPtr<MyObject> obj1 = make_ref_counted<MyObject>();
RefPtr<MyObject> obj2 = obj1; // Reference count is now 2

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WeakPtr

Non-owning pointer that automatically becomes null when the target is deleted: 
class Foo : public Weakable<Foo> {
    // ...
};

NonnullOwnPtr<Foo> owner = make<Foo>();
WeakPtr<Foo> weak = owner->make_weak_ptr();
// weak automatically becomes null when owner is destroyed

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String types

AK provides multiple string types optimized for different use cases.

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String

UTF-8 encoded, reference-counted string with short string optimization: 
// From UTF-8
auto str = String::from_utf8("Hello, World!"sv);

// String literals (compile-time)
auto str = "Hello"_string;

// Formatting
auto formatted = String::formatted("Value: {}", 42);
String can store short strings (up to 23 bytes) inline without heap allocation, making it very efficient for common use cases.

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StringView

Non-owning view over string data: 
void process(StringView text) {
    // No copying, just a pointer and length
    dbgln("Processing: {}", text);
}

String owned = "data"_string;
process(owned.bytes_as_string_view());
process("literal"sv);

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StringBuilder

Efficient string building through concatenation: 
StringBuilder builder;
builder.append("Hello "sv);
builder.append("World"sv);
builder.appendff(", the answer is {}!", 42);

auto result = builder.to_string();

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Error handling

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ErrorOr<T>

Type-safe error handling without exceptions: 
ErrorOr<String> read_file(StringView path) {
    // Return either String or Error
    return String::from_utf8(data);
}

// Using TRY macro for error propagation
ErrorOr<void> process() {
    auto content = TRY(read_file("/path/to/file"sv));
    // Use content...
    return {};
}

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Result<T, E>

Generic result type for operations that can fail: 
Result<int, ParseError> parse_number(StringView str) {
    if (str.is_empty())
        return ParseError::Empty;
    return 42;
}

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String formatting

AK provides printf-style formatting with compile-time checking. 
// Basic formatting
auto str = String::formatted("Hello, {}!", "world");

// With format specifiers
auto hex = String::formatted("0x{:04x}", 255); // "0xff"
auto aligned = String::formatted("{:>10}", "right");  // "     right"

// Debug output
dbgln("Value: {}, Hex: {:x}", 42, 42);

Type specifiers

b binary, d decimal, x hex, s string, p pointer

Alignment

< left, > right, ^ center

Width & precision

{:10} min width, {:.4} precision/max

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Utilities

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Function

Type-erased callable wrapper: 
Function<int(int, int)> operation = [](int a, int b) { return a + b; };
int result = operation(5, 3); // 8

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Time

High-resolution time with duration types: 
auto now = AK::Time::now_monotonic();
auto duration = AK::Time::from_milliseconds(500);
auto later = now + duration;

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Badge

Restrict function access to specific classes: 
class Foo {
public:
    void sensitive_operation(Badge<Manager>) {
        // Only Manager can call this
    }
};

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Source location

  • Repository: ~/workspace/source/AK/
  • Key headers: Vector.h, HashMap.h, String.h, NonnullOwnPtr.h, RefPtr.h, Optional.h
  • Documentation: ~/workspace/source/Documentation/SmartPointers.md, ~/workspace/source/Documentation/StringFormatting.md
AK is designed to have zero dependencies - it doesn’t even depend on the C++ standard library for most operations. This makes it highly portable and predictable.

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