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/**

@file

@brief C++20

@defgroup CPP20 C++20 examples

https://en.wikipedia.org/wiki/C++20

https://github.com/AnthonyCalandra/modern-cpp-features/blob/master/CPP20.md

https://en.cppreference.com/w/cpp/20

static_assert(__cplusplus >= 201707);

#if __has_include (<bit>)

#include <bit>

#endif

#include <vector>

#include <cmath>

#include <cassert>

#include <vector>

#include <map>

#include <memory>

#include <thread>

#include <sstream>

#include <experimental/array>

#if __has_include (<concepts>)

#include <concepts>

#endif

using namespace std;

/**

@defgroup lang20 Language

https://en.cppreference.com/w/cpp/language

#if __cpp_lib_three_way_comparison

static_assert(1 <=> 2 < 0 );

static_assert(2 <=> 1 > 0 );

static_assert(1 <=> 1 == 0 );

#else

#pragma message("undefined __cpp_lib_three_way_comparison")

#endif

#if __cpp_char8_t

/// https://en.cppreference.com/w/cpp/keyword/char8_t

char8_t char8;

#endif

/// https://en.cppreference.com/w/cpp/container/array/to_array

auto to_array_demo = experimental::to_array("foo");

static_assert(to_array_demo.size() == 4);

void init_20()

{

struct point { int x, y; };

struct line { point a, b; };

// https://en.cppreference.com/w/cpp/language/aggregate_initialization

#if __cplusplus > 201707

point p1 = { .x = 1 };

assert(p1.x == 1);

assert(!p1.y);

point p2 { .y { 2 } };

assert(p2.y == 2);

assert(!p2.x);

#endif

line l1 = { };

assert(!l1.a.x);

line l2 = { 1, 2 };

assert(l2.a.x == 1);

assert(l2.a.y == 2);

line l3 = { 1, 2, 3, 4 };

assert(l3.b.x == 3);

assert(l3.b.y == 4);

}

void types_20()

{

#if __cpp_lib_bit_cast

cout << typeid(bit_cast<double>(0));

#endif

}

void dynamic_memory_20()

{

/// Shared array

/// https://en.cppreference.com/w/cpp/memory/shared_ptr/make_shared

auto a = make_shared<int[10]>();

cout << typeid(decltype(a.get())).name();

static_assert(is_same_v<decltype(a.get()), int*>);

/// https://en.cppreference.com/w/cpp/container/map/contains

map<int, int> m = {{2,3}};

#if __cplusplus > 201707

assert(m.contains(2));

#endif

#if __cpp_lib_erase_if

/// [erase_if](https://en.cppreference.com/w/cpp/container/map/erase_if)

vector<int> v = {11, 12, 13};

assert(erase_if(v, [](int a) {return a >= 13;}) == 1);

assert(v.size() == 2);

#endif

}

namespace lambda {

#if __cpp_template_template_args

/// Lambda capture of parameter pack

template <typename ... Args>

auto make_lambda_with_parameter_pack_capture(Args&& ... args)

{

// parameter pack capture:

return [... args = forward<Args>(args)] {

return (... + args);

};

}

#endif

void lambda_20()

{

#if __cplusplus >= 201709

// generic lambda, operator() is a template with two parameters

auto glambda = []<class T>(T a, auto&& b) { return a < b; };

assert(glambda(1,2));

// generic lambda, operator() is a template with one parameter pack

auto f = []<typename ...Ts>(Ts&& ...ts) {

return 1;

};

assert(f(1,2,3));

struct point { int x, y; };

auto point_lambda = []<class T=point>(T&& var) {};

point_lambda({1, 2});

#if __cpp_template_template_args

assert(make_lambda_with_parameter_pack_capture(1,2,3)() == 6);

#endif

}

using namespace lambda;

/// @} lang20

/**

@defgroup templ20 Template

https://en.cppreference.com/w/cpp/language/templates

#if __cpp_concepts

/**

@defgroup conc20 Concepts

https://en.wikipedia.org/wiki/Concepts_(C++)

https://en.cppreference.com/w/cpp/language/constraints

https://en.cppreference.com/w/cpp/header/concepts

/**

@defgroup req20 'Requires' clause and expression

// Using [requires](https://en.cppreference.com/w/cpp/keyword/requires)

template <typename T> requires is_integral_v<T> T constexpr requires_demo(T a) { return a + 1; }

static_assert(requires_demo(1) == 2);

/**

requires-clause can be after function declaration and supports template overloading

template <typename T> auto constexpr requires_demo(T && a) requires is_same_v<T, double> { return 2; }

static_assert(requires_demo(0.1) == 2);

// Annotated example of complex requirement

template <class T>

requires // requires-clause

is_signed_v<T> || (is_unsigned_v<T> && ! is_void_v<void>) // constraint expression

void complex_requirement_demo() { }

/// Annotated example of requires-expression

template < class T >

requires // requires-clause

requires() // requires-expression

{ true;} // unevaluated requirements sequence

void requires_expression_demo() { }

template <class T> requires requires(T a) { a / 0; } auto constexpr what(T a) { return 1; }

static_assert(what(1) == 1);

template <class T> requires requires(T a) { a[0]; } auto constexpr what(T a) { return 2; }

static_assert(what("2") == 2);

/// @}

#if __cpp_concepts < 201907

/**

In Technical Specification a concept can be defined as function

template <typename T> concept bool integral_ct() { return is_integral_v<T>; }

template <integral_ct T> constexpr T _inc3(T a) { return a + 1; }

static_assert(_inc3(1) == 2);

// concept can replace type

template <integral_ct T> constexpr T _inc1(T a) { return a + 1; }

static_assert(_inc1<int>(1) == 2);

// can be used in generic function

constexpr auto generic_function_with_integral_concept(integral_ct v) { return v + 1; }

static_assert(generic_function_with_integral_concept(1) == 2);

integral_ct integral_var = 1; // variable defined with concept

/**

defining concept as function with requires-expression

template <typename T> concept bool integral_func_req_ct()

requires requires () { is_integral_v<T>; }

{ return true; }

template <integral_func_req_ct T> constexpr T _inc4(T a) { return a + 1; }

static_assert(_inc4(1) == 2);

template<typename T> concept compound_requirement =

requires(T x) {{x + 1} -> int;};

#endif

/**

@defgroup conc_alt20 Alternative forms of concept definition

/// trivial concepts as assignment

template <typename T> concept truism = true;

#if !__cpp_lib_concepts

/// short concept definition from a constraint directly

template <class T> concept integral = is_integral_v<T>;

#endif

/**

defining concept with requires-expression

template <class T> concept integral_req_ct = requires (T a) { is_integral_v<T>; };

template <integral_req_ct T> constexpr T _inc2(T a) { return a + 1; }

static_assert(_inc2(1) == 2);

/// @}

#else

#pragma message("undefined __cpp_concepts")

#endif

#if __cpp_lib_ranges

#include <ranges>

/// [ranges](https://en.cppreference.com/w/cpp/ranges)

struct ranges_20 {

ranges_20() {

auto data = {0, 1, 2, 3};

/// [reverse_view](https://en.cppreference.com/w/cpp/ranges/reverse_view)

ranges::reverse_view rv {data};

auto r = data | views::reverse;

// r is kind of transform_view

vector result(r.begin(), r.end());

assert(vector(rv.begin(), rv.end()) == result);

assert((result == vector{3, 2, 1, 0}));

}

} ranges_20;

#else

#pragma message("undefined __cpp_lib_ranges")

#endif

/**

@defgroup other20 Other

TODO:

https://en.cppreference.com/w/cpp/language/range-for

https://en.cppreference.com/w/cpp/language/coroutines

https://en.cppreference.com/w/cpp/language/constinit

/// @}

#include <experimental/source_location>

/// [source_location](https://en.cppreference.com/w/cpp/utility/source_location)

struct location_20 {

location_20() {

auto l = experimental::source_location::current();

basic_stringstream<char> buff;

buff << l.file_name() << ":" << l.line() << ":" << l.column() << l.function_name();

assert(buff.str().length());

}

} location_20;

int main()

{

init_20();

types_20();

dynamic_memory_20();

lambda_20();

#if __cpp_lib_jthread

jthread t([]{ });

#endif

}

/// @}

/**

@mainpage

@ref CPP20

@ref CPP17

@ref CPP14

@ref CPP11

@ref CPP03

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