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Εγκριθηκε η νέα C++20

Με την ονομασία C ++ 20, η νέα έκδοση της γλώσσας C ++ έχει λάβει ομόφωνα την τελική τεχνική έγκρισή της , την Παρασκευή 4 Σεπτεμβρίου, από την ομάδα εργασίας που είναι αφιερωμένη σε αυτήν στο πλαίσιο του Διεθνούς Οργανισμού Τυποποίησης (ISO). Σύμφωνα με τον Herb Sutter, μηχανικό της Microsoft και πρόεδρο της επιτροπής ISO C ++, η C ++ 20 θα είναι “η μεγαλύτερη έκδοση της C ++”. Αυτό το νέο πρότυπο γλώσσας, το οποίο ενημερώνεται κάθε 3 χρόνια, είναι πιο σημαντικό από τα προηγούμενα τρία. Eπίσης είναι η πρώτη τυποποιημένη έκδοση.

Νέες δυνατότητες αναμένονται από το C ++ 20

Με την ευκαιρία αυτής της σημαντικής ενημέρωσης της γλώσσας που δημιουργήθηκε το 1980 από τον Δανό επιστήμονα υπολογιστών Bjarne Stroustrup, δύο νέα χαρακτηριστικά έρχονται : modules και coroutines.

Οι coroutines και άλλες δυνατότητες C ++ 20

Οι coroutines είναι λειτουργίες που μπορούν να αναστείλουν και να συνεχίσουν την εκτέλεση τους χωρίς να τροποποιήσουν την κατάστασή τους. Στόχος τους είναι να γενικεύσουν τη χρήση υπορουτίνων σε μη προληπτικές πολλαπλές εργασίες. Σημειώστε ότι η υποστήριξη για αυτές τις κορουτίνες στην τυπική βιβλιοθήκη έχει προγραμματιστεί για την έκδοση C ++ 23.

Μεταξύ των άλλων νέων δυνατοτήτων που αναμένονται από το C ++ 20, βρίσκουμε επίσης την παρουσία του library synchronization και νέων αλγορίθμων τηλεμετρίας.

Αναλυτικά τα νέα features

New language features

Feature test macros
3-way comparison operator <=> and operator==() = default
designated initializers
init-statements and initializers in range-for
char8_t
[[no_unique_address]]
[[likely]]
[[unlikely]]
pack-expansions in lambda init-captures
removed the requirement to use typename to disambiguate types in many contexts
consteval, constinit
further relaxed constexpr
signed integers are 2’s complement
aggregate initialization using parentheses
Coroutines
Modules
Constraints and concepts
Abbreviated function templates
DR: array new can deduce array size

New library features

Library features

Library feature-test macros
Formatting library
Calendar and Time Zone library
source_location
span
endian
array support for make_shared
remove_cvref
to_address
floating point atomics, shared_ptr atomics
thread-coordination classes: barrier, latch, and counting_semaphore
jthread and thread cancellation classes: stop_token, stop_source, and stop_callback
basic_osyncstream
u8string and other char8_t uses
constexpr for , ,
string::starts_with / ends_with and string_view::starts_with / ends_with
assume_aligned
bind_front
c8rtomb/mbrtoc8
make_obj_using_allocator etc
make_shared_for_overwrite/make_unique_for_overwrite
heterogeneous lookup in unordered associative containers
polymorphic_allocator with additional member functions and byte as its default template argument
execution::unseq
midpoint and lerp
ssize
is_bounded_array, is_unbounded_array
Ranges
uniform container erasure: std::erase/std::erase_if, e.g. std::erase(std::list) or erase_if(std::map) etc
Mathematical constants in

Παράδειγμα απο την C++20

/**
 @file
 @brief C++20
 @defgroup CPP20 C++20 examples
 [C++20](https://en.wikipedia.org/wiki/C++20)
 [Modern Cpp20 features](https://github.com/AnthonyCalandra/modern-cpp-features/blob/master/CPP20.md)
 https://en.cppreference.com/w/cpp/20
 @{
*/
static_assert(__cplusplus >= 201707);
#include 
#include 
#if __has_include ()
#include 
#endif
#include 
#include 
#include 
#include 
#include 
#include 
#if __cpp_impl_coroutine
#include 
#endif
#include 
#include 
#if __has_include ()
#include 
#endif
using namespace std;
/**
 @defgroup lang20 Language
 [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
/// [char8_t](https://en.cppreference.com/w/cpp/keyword/char8_t)
char8_t char8;
#endif
/// [to_array](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; };
	// [aggregate_initialization](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 { {} , 2 };
	assert(p2.y == 2);
	assert(!p2.x);
#endif
#if __cpp_aggregate_paren_init >= 201902
	int a[] (0, 1, 2);
	assert(a[2] == 2);
	line l2 = { 1, 2 };
	assert(l2.a.x == 1);
	assert(l2.a.y == 2);
#endif
	line l1 = { };
	assert(!l1.a.x);
	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(0));
#endif
}
void dynamic_memory_20()
{
	/// Shared array
	/// [make_shared](https://en.cppreference.com/w/cpp/memory/shared_ptr/make_shared)
	auto a = make_shared();
	static_assert(is_same_v);
	/// [contains](https://en.cppreference.com/w/cpp/container/map/contains)
	map m = {{2,3}};
#if __cplusplus > 201707 && __GNUG__ > 8
	assert(m.contains(2));
#endif
#if __cpp_lib_erase_if
	/// [erase_if](https://en.cppreference.com/w/cpp/container/map/erase_if)
	vector 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 && __GNUG__ > 8
/// [Lambda capture of parameter pack](https://en.cppreference.com/w/cpp/language/lambda#Lambda_capture)
template 
auto make_lambda_with_parameter_pack_capture(Args&& ... args)
{
	return [... args = forward(args)] {
		return (... + args);
	};
}
#endif
void lambda_20()
{
#if __cplusplus >= 201709
	// generic lambda, operator() is a template with two parameters
	auto glambda = [](T a, auto&& b) { return a < b; };
	assert(glambda(1,2));
	// generic lambda, operator() is a template with one parameter pack
	auto f = [](Ts&& ...ts) {
		return 1;
	};
	assert(f(1,2,3));
	struct point { int x, y; };
	auto point_lambda = [](T&& var) {};
	point_lambda({1, 2});
	#if __cpp_template_template_args && __GNUG__ > 8
	assert(make_lambda_with_parameter_pack_capture(1,2,3)() ==  6);
	#endif
#endif
}
}
using namespace lambda;

/// @} lang20
/**
 @defgroup templ20 Template
 [templates](https://en.cppreference.com/w/cpp/language/templates)
 @{
*/
#if __cpp_concepts
/**
 @}
 @defgroup conc20 Concepts
 https://en.wikipedia.org/wiki/Concepts_(C++)
 [constraints](https://en.cppreference.com/w/cpp/language/constraints)
 [concepts](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  requires is_integral_v 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  auto constexpr requires_demo(T && a) requires is_same_v { return 2; }
static_assert(requires_demo(0.1) == 2);
// Annotated example of complex requirement
template 
requires // requires-clause
is_signed_v || (is_unsigned_v && ! is_void_v) // 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  requires requires(T a) { a / 0; } auto constexpr what(T a) { return 1; }
static_assert(what(1) == 1);
template  requires requires(T a) { a[0]; } auto constexpr what(T a) { return 2; }
static_assert(what("2") == 2);
/// @}

/**
 @defgroup conc_def_20 Concept definitions
 @{
 */
/// trivial concepts as assignment
template  concept truism = true;
#if !__cpp_lib_concepts
/// short concept definition from a constraint directly
template  concept integral = is_integral_v;
#endif
/**
  defining concept with requires-expression
 */
template  concept integral_req_ct = requires (T a) { is_integral_v; };
template  constexpr T _inc2(T a) { return a + 1; }
static_assert(_inc2(1) == 2);
/**
  [Compound_Requirements](https://en.cppreference.com/w/cpp/language/constraints#Compound_Requirements)
  [convertible_to](https://en.cppreference.com/w/cpp/concepts/convertible_to)
 */
template concept compound_requirements =
requires(T x) {
	{x + 1} -> convertible_to;
	{x * 2} -> same_as;
};

/// @}
/// @}
#else
#pragma message("undefined __cpp_concepts")
#endif
/**
 @defgroup cor20 Coroutines
 @{
	[coroutine](https://en.cppreference.com/w/cpp/coroutine)
	[coroutines](https://en.cppreference.com/w/cpp/language/coroutines)
 */
#if __cpp_impl_coroutine
auto switch_to_new_thread(jthread& out)
{
	struct awaitable {
		jthread* p_out;
		bool await_ready() { return false; }
		void await_suspend(coroutine_handle<> h) {
			jthread& out = *p_out;
			if (out.joinable())
				throw runtime_error("Output jthread parameter not empty");
			out = jthread([h] { h.resume(); });
		}
		void await_resume() {}
	};
	return awaitable{&out};
}
struct task {
	struct promise_type {
		struct task get_return_object() { return {}; }
		suspend_never initial_suspend() { return {}; }
		suspend_never final_suspend() noexcept { return {}; }
		void return_void() {}
		void unhandled_exception() {}
	};
};
struct task resuming_on_new_thread(jthread& out)
{
	auto starting_tid = this_thread::get_id();
	// suspends coroutine
	co_await switch_to_new_thread(out); ///< [co_await](https://en.cppreference.com/w/cpp/keyword/co_await)
	// awaiter is destroyed here
	assert(this_thread::get_id() != starting_tid);
}
void coroutine_demo()
{
	jthread out;
	resuming_on_new_thread(out);
}
#else
void coroutine_demo() {}
#pragma message("undefined __cpp_impl_coroutine")
#endif
/// @}
/**
 @defgroup other20 Other
 @{
  TODO:
  [range-for](https://en.cppreference.com/w/cpp/language/range-for)
 */
#if __cpp_lib_ranges
#include 
/// [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)
#if __clang_major__ != 10
		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}));
#endif
	}
} ranges_20;
#else
#pragma message("undefined __cpp_lib_ranges")
#endif
#include 
/// [source_location](https://en.cppreference.com/w/cpp/utility/source_location)
struct location_20 {
	location_20() {
		auto l = experimental::source_location::current();
		basic_stringstream buff;
		buff << l.file_name() << ":" << l.line() << ":" << l.column() << l.function_name();
		assert(buff.str().length());
	}
} location_20;
/**
 [functional](https://en.cppreference.com/w/cpp/header/functional)
 */
void functional_20()
{
	/// [bind_front](https://en.cppreference.com/w/cpp/utility/functional/bind_front)
	auto constexpr plus_one = std::bind_front(std::plus(), 1);
	static_assert(plus_one(2) == 3);
}
/// @} other20
int main()
{
	init_20();
	types_20();
	dynamic_memory_20();
	lambda_20();
#if __cpp_lib_jthread
	jthread t([]{ });
#endif
	coroutine_demo();
	functional_20();
}
/// @}
/**
 @mainpage
 @ref CPP20
 @ref CPP17
 @ref CPP14
 @ref CPP11
 @ref CPP03
*/

Εγκριθηκε η νέα C++20

Νέες δυνατότητες αναμένονται από το C ++ 20

Οι coroutines και άλλες δυνατότητες C ++ 20