fixes for docs and tests

example/examples.cpp

@@ -0,0 +1,110 @@
+// Copyright 2016-2020 Antony Polukhin
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See the accompanying file LICENSE_1_0.txt
+// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
+
+#include <cassert>
+
+
+//[pfr_sample_printing
+/*`
+    The following example shows how to customize printing and write your own testing helper for structures:
+*/
+#include <boost/pfr.hpp>
+#include <iostream>
+
+namespace my_testing {
+
+template <class T>
+void print_each(std::ostream& out, const T& v) { out << v; }
+void print_each(std::ostream& out, std::uint8_t v) { out << static_cast<unsigned>(v); }
+void print_each(std::ostream& out, std::int8_t v) { out << static_cast<int>(v); }
+
+template <class T>
+void print(const T& value) {
+    const char* sep = "";
+
+    boost::pfr::for_each_field(value, [&](const auto& v) {
+        std::cerr << std::exchange(sep, ", ");
+        print_each(std::cerr, v);
+    });
+}
+
+/// Usage:
+///     struct foo {std::uint8_t a, b;};
+///     foo get_foo();
+///     ...
+///     test_eq(foo{42, 22}, get_foo());
+///
+/// Output:
+///     42, 22 != 42, 24
+template <class T>
+void test_eq(const T& x, const T& y) {
+    using namespace boost::pfr::ops;
+    if (x == y) return;
+
+    print(x);
+    std::cerr << " != ";
+    print(y);
+}
+
+} // namespace my_testing
+//] [/pfr_sample_printing]
+
+
+//[pfr_example_get
+/*`
+    The following example shows how to access structure fields by index using [funcref boost::pfr::get].
+
+    Let's define some structure:
+*/
+#include <boost/pfr/core.hpp>
+
+struct foo {            // defining structure
+    int some_integer;
+    char c;
+};
+
+/*`
+    We can access fields of that structure by index:
+*/
+foo f {777, '!'};
+auto& r1 = boost::pfr::get<0>(f); // accessing field with index 0, returns reference to `foo::some_integer`
+auto& r2 = boost::pfr::get<1>(f); // accessing field with index 1, returns reference to `foo::c`
+//] [/pfr_example_get]
+
+//[pfr_example_tuple_size
+/*`
+    The following example shows how to count fields using [classref boost::pfr::tuple_size].
+*/
+#include <boost/pfr/core.hpp>
+
+struct foo2 {            // defining structure
+    int some_integer;
+    char c;
+    short some_other_field;
+};
+
+
+static_assert(
+    boost::pfr::tuple_size<foo2>::value        // returns total count of fields in `foo2`
+    == 3, ""
+);
+
+static_assert(
+    boost::pfr::tuple_size<int[100]>::value    // works with arrays too!
+    == 100, ""
+);
+//] [/pfr_example_tuple_size]
+
+
+struct foo_printing_test {std::uint8_t a, b;};
+foo_printing_test get_foo_printing_test() { return foo_printing_test{42, 24}; }
+
+int main() {
+    my_testing::test_eq(
+        foo_printing_test{42, 22},
+        get_foo_printing_test()
+    );
+}