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103 lines
2.4 KiB
C++
103 lines
2.4 KiB
C++
// Copyright 2016 Antony Polukhin
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// Distributed under the Boost Software License, Version 1.0.
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// (See the accompanying file LICENSE_1_0.txt
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// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
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#include <cassert>
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//[pfr_example_get
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/*`
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The following example shows how to access structure fields by index using [funcref boost::pfr::flat_get].
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Let's define some structure:
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*/
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#include <boost/pfr/flat/core.hpp>
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struct foo { // defining structure
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int some_integer;
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char c;
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};
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/*`
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We can access fields of that structure by index:
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*/
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foo f {777, '!'};
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auto& r1 = boost::pfr::flat_get<0>(f); // accessing field with index 0, returns reference to `foo::some_integer`
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auto& r2 = boost::pfr::flat_get<1>(f); // accessing field with index 1, returns reference to `foo::c`
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//] [/pfr_example_get]
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//[pfr_example_flat_tuple_size
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/*`
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The following example shows how to count fields using [classref boost::pfr::flat_tuple_size].
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*/
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#include <boost/pfr/flat/core.hpp>
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struct foo2 { // defining structure
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int some_integer;
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char c;
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short some_other_field;
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};
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static_assert(
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boost::pfr::flat_tuple_size<foo2>::value // returns total count of fields in `foo2`
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== 3, ""
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);
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static_assert(
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boost::pfr::flat_tuple_size<int[100]>::value // works with arrays too!
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== 100, ""
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);
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//] [/pfr_example_flat_tuple_size]
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//[pfr_example_flattening
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/*`
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[warning All the functions and metafunctions in Boost.PFR that start with `flat_` represent template parameter type as flat structure without static members! ]
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Take a look at the `struct my_struct`:
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*/
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struct my_struct_nested { short a1; int a2; };
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struct my_struct {
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int a0;
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static const int cvalue = 1000;
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my_struct_nested nested;
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short a3_a4[2];
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};
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/*` It will be flattened and represented as: */
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struct my_struct_flat {
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int a0;
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short a1;
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int a2;
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short a3;
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short a4;
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};
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//] [/pfr_example_flattening]
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void example_get() {
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//[pfr_example_flattening_2
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/*`
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It means, that:
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*/
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boost::pfr::flat_get<2>(my_struct{}); // ... will return `my_struct::my_struct_nested::a2` field.
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boost::pfr::flat_get<3>(my_struct{}); // ... will return `my_struct::a3_a4[0]` field.
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/*` Exactly the same story with arrays: */
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int i[2][2] = {{10, 11}, {12, 13} };
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const int& r = boost::pfr::flat_get<1>(i);
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assert(r == 11);
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//] [/pfr_example_flattening_2]
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(void)r;
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}
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int main() {
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example_get();
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}
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