C++20: Get the Details

Table of Contents....3

Reader Testimonials....11

Introduction....13

Conventions....14

Special Fonts....14

Special Boxes....14

Source Code....15

Compilation of the Programs....15

How should you read the Book?....16

Personal Notes....17

Acknowledgments....17

About Me....18

About C++....20

Historical Context....21

C++98....21

C++03....22

TR1....22

C++11....22

C++14....22

C++17....23

Standardization....24

Stage 3....25

Stage 2....25

Stage 1....25

A Quick Overview of C++20....27

C++20....28

The Big Four....29

Concepts....29

Modules....31

The Ranges Library....32

Coroutines....33

Core Language....36

Three-Way Comparison Operator....36

Designated Initialization....37

consteval and constinit....40

Template Improvements....41

Lambda Improvements....42

New Attributes....43

The Standard Library....44

std::span....44

Container Improvements....45

Arithmetic Utilities....45

Calendar and Time Zones....46

Formatting Library....47

Concurrency....49

Atomics....49

Semaphores....50

Latches and Barriers....50

Cooperative Interruption....51

std::jthread....53

Synchronized Outputstreams....55

The Details....58

Core Language....59

Concepts....60

Two Wrong Approaches....60

Advantages of Concepts....67

The long, long History....68

Use of Concepts....69

Constrained and Unconstrained Placeholders....83

Abbreviated Function Templates....86

Predefined Concepts....92

Defining Concepts....100

Application....110

Modules....126

Why do we need Modules?....126

Advantages....135

A First Example....136

Compilation and Use....139

Export....141

Guidelines for a Module Structure....143

Module Interface Unit and Module Implementation Unit....144

Submodules and Module Partitions....148

Templates in Modules....154

Module Linkage....157

Header Units....160

Three-Way Comparison Operator....162

Ordering before C++20....162

Ordering since C++20....164

Comparision Categories....168

The Compiler-Generated Spaceship Operator....171

Rewriting Expressions....176

User-Defined and Auto-Generated Comparison Operators....180

Designated Initialization....184

Aggregate Initialization....184

Named Initialization of Class Members....186

consteval and constinit....192

consteval....192

constinit....194

Function Execution....195

Variable Initialization....197

Solving the Static Initialization Order Fiasco....199

Template Improvements....206

Conditionally Explicit Constructor....206

Non-Type Template Parameters....210

Lambda Improvements....214

Template Parameter for Lambdas....214

Detection of the Implicit Copy of the this Pointer....220

Lambdas in an Unevaluated Context and Stateless Lambdas can be Default-Constructed and Copy-Assigned....222

New Attributes....228

[[nodiscard("reason")]]....229

[[likely]] and [[unlikely]]....235

[[no_unique_address]]....236

Further Improvements....239

volatile....239

Range-based for loop with Initializers....241

Virtual constexpr function....243

The new Character Type of UTF-8 Strings: char8_t....244

using enum in Local Scopes....246

Default Member Initializers for Bit Fields....248

The Standard Library....250

The Ranges Library....251

The Concepts Ranges and Views....252

Direct on the Container....254

Function Composition....260

Lazy Evaluation....262

Define a View....266

A Flavor of Python....271

std::span....279

Static versus Dynamic Extent....279

Automatically Deduces the Size of a Contiguous Sequence of Objects....281

Create a std::span from a Pointer and a Size....283

Modifying the Referenced Objects....285

Addressing std::span Elements....286

A Constant Range of Modifiable Elements....289

Container Improvements....292

constexpr Containers and Algorithms....292

std::array....294

Consistent Container Erasure....296

contains for Associative Containers....302

String prefix and suffix checking....305

Arithmetic Utilities....309

Safe Comparison of Integers....309

Mathematical Constants....315

Midpoint and Linear Interpolation....318

Bit Manipulation....320

Calendar and Time Zones....328

Time of day....330

Calendar Dates....333

Time Zones....354

Formatting Library....365

Format String....367

User-Defined Types....378

Further Improvements....386

std::bind_front....386

std::is_constant_evaluated....389

std::source_location....391

Concurrency....394

Coroutines....395

A Generator Function....396

Characteristics....399

The Framework....403

Awaitables and Awaiters....406

The Workflows....410

co_return....414

co_yield....417

co_await....421

Atomics....432

std::atomic_ref....432

Atomic Smart Pointer....442

std::atomic_flag Extensions....448

std::atomic Extensions....458

Semaphores....463

Latches and Barriers....470

std::latch....471

std::barrier....477

Cooperative Interruption....482

std::stop_source....483

std::stop_token....484

std::stop_callback....485

std::jthread....493

Automatically Joining....494

Cooperative Interruption of a std::jthread....497

Synchronized Output Streams....501

Case Studies....511

Fast Synchronization of Threads....512

Condition Variables....513

std::atomic_flag....515

std::atomic....520

Semaphores....523

All Numbers....525

Variations of Futures....526

A Lazy Future....529

Execution on Another Thread....533

Modification and Generalization of a Generator....539

Modifications....544

Generalization....548

Various Job Workflows....552

The Transparent Awaiter Workflow....552

Automatically Resuming the Awaiter....556

Automatically Resuming the Awaiter on a Separate Thread....559

Epilogue....564

Further Information....566

C++23 and Beyond....567

C++23....568

The Coroutines Library....568

Modularized Standard Library for Modules....588

Executors....591

The Network Library....597

C++23 or Later....599

Contracts....599

Reflection....605

Pattern Matching....609

Further Information about C++23....612

Feature Testing....614

Glossary....630

Callable....630

Callable Unit....630

Concurrency....630

Critical Section....630

Data Race....631

Deadlock....631

Eager Evaluation....631

Executor....631

Function Objects....632

Lambda Expressions....632

Lazy Evaluation....633

Lock-free....633

Lost Wakeup....633

Math Laws....633

Memory Location....634

Memory Model....634

Non-blocking....634

Object....634

Parallelism....634

Predicate....635

RAII....635

Race Conditions....635

Regular....635

Scalar....636

SemiRegular....636

Spurious Wakeup....636

The Big Four....636

The Big Six....637

Thread....637

Time Complexity....637

Translation Unit....638

Undefined Behavior....638

Index....639

My book C++20 is both a tutorial and a reference. It teaches you C++20 and provides you with the details of this new thrilling C++ standard. The thrill factor is mainly due to the big four of C++20:

• Concepts change the way we think about and program with templates. They are semantic categories for template parameters. They enable you to express your intention directly in the type system. If something goes wrong, the compiler gives you a clear error message.
• Modules overcome the restrictions of header files. They promise a lot. For example, the separation of header and source files becomes as obsolete as the preprocessor. In the end, we have faster build times and an easier way to build packages.
• The new ranges library supports performing algorithms directly on the containers, composing algorithms with the pipe symbol, and applying algorithms lazily on infinite data streams.
• Thanks to coroutines, asynchronous programming in C++ becomes mainstream. Coroutines are the basis for cooperative tasks, event loops, infinite data streams, or pipelines.

Of course, this is not the end of the story. Here are more C++20 features:

•  Auto-generated comparison operators
• Calendar and time-zone libraries
• Format library
• Views on contiguous memory blocks
• Improved, interruptible threads
• Atomic smart pointers
• Semaphores
• Coordination primitives such as latches and barriers