Chapter 3 examples

chapter_03/examples/CMakeLists.txt

+cmake_minimum_required(VERSION 3.28)
+set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+project(cxx_course_examples CXX)
+
+
+FILE (GLOB sources ./ *.cc)
+foreach(source ${sources})
+    get_filename_component(withoutext "${source}" NAME_WE)
+    add_executable("${withoutext}" "${source}")
+endforeach()
+
+

chapter_03/examples/addables.cc

+#include <iostream>
+#include <string>
+#include <concepts>
+
+template <class T>
+concept Addable = requires(T a, T b) {
+    { a + b } -> std::convertible_to<T>;
+};
+
+auto aggregate(Addable auto... args)
+{
+    return (args + ...);
+}
+
+auto main() -> int
+{
+    using namespace std::string_literals;
+    std::cout << "aggregate(1, 2, 3, 4, 5) = "
+              << aggregate(1, 2, 3, 4, 5) << "\n";
+    std::cout << R"aw(aggregate("|-"s, "-|"s) = )aw"
+                << aggregate("|-"s, "-|"s) << "\n";
+}
+

chapter_03/examples/fold_xpr_demo2.cc

+#include <iostream>
+#include <string>
+#include <vector>
+
+auto add_up(auto... args)
+{
+    return (args + ...);
+}
+
+template <typename T>
+void push_back(std::vector<T> &v, auto ... args) {
+    (v.push_back(args), ...);
+}
+
+auto main() -> int
+{
+    using namespace std;
+    string firstname{ "Steve" }, lastname{ "Rogers" };
+    cout << add_up(1, 2, 3, 4, 5) << "\n";
+    cout << add_up(firstname, " ", lastname) << "\n";
+
+    std::vector<double> q{0.0};
+    push_back(q, 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7, 8.8);
+    for (auto d : q) cout << d << "\n";
+}

chapter_03/examples/fold_xpr_demo3.cc

+#include <vector>
+#include <iostream>
+#include <algorithm>
+#include <ranges>
+#include <string>
+#include "print_tuple.hh"
+
+auto max_of_multiple(auto ... containers)
+{
+    return std::make_tuple(std::ranges::max(containers) ...);
+}
+
+auto main() -> int
+{
+    std::vector v1{8.2, 84., 9.1, 33.1, 9.33, 8.2, 8.3};
+    std::vector v2{9,1,2,8,3,1,4,2,0,8,1};
+    std::vector<std::string> v3{"Compact", "code", "with", "fold", "expressions"};
+    std::cout << max_of_multiple(v1, v2, v3) << "\n";
+}
+

chapter_03/examples/fold_xpr_demo4.cc

+#include <vector>
+#include <iostream>
+#include <ranges>
+#include <algorithm>
+#include "range_output.hh"
+
+auto conv(const std::vector<double>& inp, auto ... shift)
+{
+    namespace sr = std::ranges;
+    namespace sv = std::views;
+    std::vector<double> out(inp.size(), 0.);
+    auto res_exp = sv::iota(0, static_cast<int>(inp.size())) 
+        | sv::transform([inp, shift...](auto index){
+            auto S = inp.size();
+            return (inp[(index + shift) > 0 ? (index + shift) % S : S + (index + shift) % S] + ...) 
+                    / (sizeof ... (shift));
+        }); 
+
+    sr::copy(res_exp, out.begin());
+    return out;
+}
+
+auto main() -> int
+{
+    std::vector v(21UL, 0.);
+    v[10] = 1.0;
+    for (auto i = 0UL; i < 10; ++i) {
+        v = conv(v, 0, 1, 2);
+        std::cout << "After round " << i << ", v = " << output::comma_separated << v << "\n";
+    }
+}
+

chapter_03/examples/foldex.cc

+#include <iostream>
+#include <string>
+#include <vector>
+
+template <typename... Args>
+auto add_up(Args... args)
+{
+    return (args + ...);
+}
+
+template <typename T, typename... Args>
+void push_back(std::vector<T> &v, Args ... args) {
+    (v.push_back(args), ...);
+}
+
+auto main() -> int
+{
+    using namespace std;
+    string firstname{ "Stephen" }, lastname{ "Hawking" };
+    cout << add_up(1, 2, 3, 4, 5) << "\n";
+    cout << add_up(firstname, " ", lastname) << "\n";
+
+    std::vector<double> q{0.0};
+    push_back(q, 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7, 8.8);
+    for (auto d : q) cout << d << "\n";
+}
+

chapter_03/examples/foldex_3.cc

+// examples/foldex_3.cc
+#include <algorithm>
+template <class First, class... Args>
+auto min(First first, Args... args)
+{
+    First retval = first;
+    ((retval = std::min(retval, args)), ...);
+    return retval;
+}
+int main()
+{
+    return min(8, 3, 4, 7, 2, 7) + min(2, 3, 9, 1);
+}

chapter_03/examples/gcd_w_concepts.cc

+#include <iostream>
+#include <type_traits>
+
+template <class T>
+concept Integral = std::is_integral_v<T>;
+
+constexpr auto gcd(Integral auto a, Integral auto b)
+{
+    if (b == 0)
+        return a;
+    return gcd(b, a % b);
+}
+auto main() -> int
+{
+    // Wont compile, until both the following arguments
+    // are changed into integral types.
+    std::cout << gcd(149935, 47295.) << "\n";
+}

chapter_03/examples/generic_func1.cc

+#include <iostream>
+#include <string>
+
+auto f(auto i1, auto i2)
+{
+    return i1 + i2;
+}
+
+// Same as above, but enforce that the parameters have the same type
+template <class T>
+auto g(T i1, T i2)
+{
+    return i1 + i2;
+}
+
+int main()
+{
+    using namespace std::string_literals;
+    std::cout << f(1, 2) << "\n";
+    std::cout << f(1.2, 2.2) << "\n";
+    std::cout << f("1"s, "2"s) << "\n";
+    //std::cout << f("1"s, 2) << "\n"; // Does not work
+    std::cout << g("1"s, 2) << "\n"; // Does not work, but better errors
+}
+

chapter_03/examples/generic_func2.cc

+#include <iostream>
+#include <string>
+
+// Same as above, but enforce that the parameters have the same type
+template <class T>
+auto f(T i1, T i2)
+{
+    return i1 + i2;
+}
+
+auto main() -> int
+{
+    using namespace std::string_literals;
+    std::cout << f("1", "2") << "\n"; 
+    // Does not work, because it's an invalid use of the function f. We wrote that for things which are addable.
+    // How did we try to indicate this intention of "addability" of the arguments ?
+    // Answer : We didn't!
+    // If the function had been 50 lines instead of 1, the real error would be very hard to
+    // decipher. There is an assumption regarding incoming arguments in our function template,
+    // and we did not specify that assumption anywhere. How does one indicate such constraints ?
+    // Answer(C++20) : concepts
+    // Answer(C++ < C++20) : std::enable_if, type_traits and some acrobatic programming.
+}
+

chapter_03/examples/generic_func3.cc

+#include <iostream>
+#include <string>
+#include <concepts>
+
+template <class T>
+concept Addable = requires(T a, T b) {
+    { a + b } -> std::convertible_to<T>;
+};
+
+auto f(Addable auto i1, Addable auto i2)
+{
+    return i1 + i2;
+}
+
+int main()
+{
+    using namespace std::string_literals;
+    std::cout << f(1, 2) << "\n"; 
+    std::cout << f("1"s, "2"s) << "\n"; 
+    std::cout << f("1", "2") << "\n"; 
+}
+

chapter_03/examples/generic_func4.cc

+#include <iostream>
+#include <string>
+
+template <class T>
+concept Addable = requires(T a, T b) {
+    { a + b } ;
+};
+
+
+template <class T> concept NotAddable = not Addable<T>;
+
+auto f(Addable auto i1, Addable auto i2)
+{
+    std::cout << "(using version of function f with Addable parameters) ... ";
+    return i1 + i2;
+}
+
+auto f(NotAddable auto i1, NotAddable auto i2)
+{
+    std::cout << "(using version of function f with NotAddable parameters) ... ";
+    return i1;
+}
+
+int main()
+{
+    using namespace std::string_literals;
+    std::cout << "f(1, 2) --> " << f(1, 2) << "\n"; 
+    std::cout << R"(f("1"s, "2"s) --> )" << f("1"s, "2"s) << "\n"; 
+    std::cout << R"(f("1", "2") --> )" << f("1", "2") << "\n"; 
+}
+

chapter_03/examples/no_textsub.cc

+template <unsigned N> constexpr unsigned fact = N * fact<N-1>;
+template <> constexpr unsigned fact<0> = 1U;
+static_assert(fact<7> == 5040);
+template <class A, class B>
+constexpr auto are_same = false;
+template <class A>
+constexpr auto are_same<A, A> = true;
+//static_assert(are_same<int, unsigned int>);
+using Integer = int;
+static_assert(are_same<int, Integer>);
+auto main() -> int {}
+

chapter_03/examples/overload_w_concepts.cc

+// examples/overload_w_concepts.cc
+#include <print>
+#include <concepts>
+#include <string>
+#include <typeinfo>
+
+template <class N> concept Number = std::is_floating_point_v<N> || std::is_integral_v<N>;
+template <class N> concept NotNumber = not Number<N>; 
+
+void proc(Number auto&& x) 
+{
+    std::print("Called proc for numbers with {} of typeid {}\n", x, typeid(x).name());
+}
+void proc(NotNumber auto&& x) 
+{
+    std::print("Called proc for non-numbers with {} of typeid {}\n", x, typeid(x).name());
+}
+
+auto main() -> int
+{
+    using namespace std::string_literals;
+    proc(-1);
+    proc(88UL);
+    proc("0118 999 88191 9119725 3");
+    proc(3.141);
+    proc("eighty"s);
+}
+

chapter_03/examples/print_tuple.cc

+#include <iostream>
+#include <string>
+#include <tuple>
+
+template <int idx, int MAX, typename... Args>
+struct PRINT_TUPLE {
+    static void print(std::ostream& strm, const std::tuple<Args...>& t)
+    {
+        strm << std::get<idx>(t) << (idx + 1 == MAX ? "" : ", ");
+        PRINT_TUPLE<idx + 1, MAX, Args...>::print(strm, t);
+    }
+};
+
+template <int MAX, typename... Args>
+struct PRINT_TUPLE<MAX, MAX, Args...> {
+    static void print(std::ostream& strm, const std::tuple<Args...>& t)
+    {
+    }
+};
+
+template <typename... Args>
+std::ostream& operator<<(std::ostream& strm, const std::tuple<Args...>& t)
+{
+    strm << "[";
+    PRINT_TUPLE<0, sizeof...(Args), Args...>::print(strm, t);
+    return strm << "]";
+}
+
+auto main() -> int
+{
+    std::tuple<int, std::string, double, int, double > t{23,"abc",3.141, 3, 2.718};
+    std::cout << t << "\n";
+}

chapter_03/examples/print_tuple_cxx17.cc

+#include <iostream>
+#include <string>
+#include <tuple>
+
+template <int idx, int MAX, typename... Args>
+struct PRINT_TUPLE {
+    static void print(std::ostream& strm, const std::tuple<Args...>& t)
+    {
+        if
+            constexpr(idx < MAX)
+            {
+                strm << std::get<idx>(t);
+                if
+                    constexpr((idx + 1) < MAX) strm << ", ";
+                PRINT_TUPLE<idx + 1, MAX, Args...>::print(strm, t);
+            }
+    }
+};
+
+template <typename... Args>
+auto operator<<(std::ostream& strm, const std::tuple<Args...>& t) -> std::ostream&
+{
+    strm << "[";
+    PRINT_TUPLE<0, sizeof...(Args), Args...>::print(strm, t);
+    return strm << "]";
+}
+
+auto main() -> int
+{
+    std::tuple<int, std::string, double, int, double> t{ 23, "abc", 3.141, 3, 2.718 };
+    std::cout << t << "\n";
+}

chapter_03/examples/print_tuple_cxx23.cc

+#include <print>
+#include <tuple>
+#include <string_view>
+
+auto main() -> int
+{
+    using namespace std::literals;
+    std::tuple t{0.1, 11, "eleven hundred"sv};
+    std::print("{}\n", t);
+}
+

chapter_03/examples/print_tuple_foldex.cc

+#include <tuple>
+#include <iostream>
+#include <iomanip>
+
+template <class ... Args>
+auto operator<<(std::ostream & strm, const std::tuple<Args...> & t) -> std::ostream & 
+{
+    using namespace std;
+    auto print_one = [&strm](const auto & onearg) -> ostream & {
+        using bare_type = remove_cv_t<remove_reference_t<decltype(onearg)>>;
+        if constexpr (is_same_v<bare_type, string>)
+            strm << quoted(onearg);
+        else
+            strm << onearg;
+        return strm;
+    };
+    auto print_components = [&](const auto & ... args){
+       ((print_one(args) << ", "), ...);
+    };
+    strm << "[";
+    apply(print_components, t);
+    return strm <<"]";
+}
+
+auto main() -> int
+{
+    std::tuple t1{1, "one"};
+    std::tuple t2{2, "two", "II", 2.0};
+    std::cout << t1 << "\t" << t2 << "\n";
+}
+

chapter_03/examples/static_assert0.cc

+auto advance(unsigned long L) -> double
+{
+    static_assert(sizeof(L) >= 8, "long must be at least 8 bytes. ");
+    //Bit manipulation assuming "long" is at least 8 bytes
+    return static_cast<double>(L);
+}
+auto main() -> int {}

chapter_03/examples/static_assert1.cc

+auto advance(unsigned long i) -> double
+{
+    static_assert(sizeof(i) >= 8, "long must be bigger than 8 bytes");
+    return 0.;
+}
+auto main() -> int {}
+