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dc56f6cebc
Also - remove useless value_type alias in String since it's not a Constant - document why the interface is so minimal
68 lines
1.9 KiB
C++
68 lines
1.9 KiB
C++
/*
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@copyright Louis Dionne 2015
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#include <boost/hana/core/is_a.hpp>
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#include <boost/hana/functional/compose.hpp>
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#include <boost/hana/functional/demux.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/map.hpp>
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#include <boost/hana/pair.hpp>
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#include <boost/hana/string.hpp>
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#include <boost/hana/tuple.hpp>
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#include <boost/hana/type.hpp>
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#include <cstdio>
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using namespace boost::hana;
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constexpr auto formats = make_map(
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make_pair(type<int>, string<'%', 'd'>),
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make_pair(type<float>, string<'%', 'f'>),
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make_pair(type<char const*>, string<'%', 's'>)
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);
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struct concat_strings {
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template <char ...s1, char ...s2>
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constexpr auto operator()(_string<s1...>, _string<s2...>) const
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{ return string<s1..., s2...>; }
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};
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template <typename ...Tokens>
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constexpr auto format(Tokens ...tokens_) {
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auto tokens = make_tuple(tokens_...);
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// If you don't care about constexpr-ness of `format`, you
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// can use this lambda instead of `demux(...)(...)`:
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//
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// [](auto token) {
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// return from_just(find(formats, decltype_(token)));
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// }
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auto format_string_tokens = adjust_if(tokens,
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compose(not_, is_a<String>),
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demux(from_just)(compose(partial(find, formats), decltype_))
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);
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auto format_string = fold.left(format_string_tokens, string<>, concat_strings{});
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auto variables = filter(tokens, compose(not_, is_a<String>));
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return prepend(format_string, variables);
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}
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int main() {
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int a = 1;
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float b = 1.3;
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char const* c = "abcdef";
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auto args = format(
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BOOST_HANA_STRING("first="), a
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, BOOST_HANA_STRING(" second="), b
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, BOOST_HANA_STRING(" third="), c
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);
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unpack(args, [](auto fmt, auto ...args) {
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std::printf(to<char const*>(fmt), args...);
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});
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}
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