libpqxx 7.7.5
separated_list.hxx
1/* Helper similar to Python's `str.join()`.
2 *
3 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/separated_list instead.
4 *
5 * Copyright (c) 2000-2023, Jeroen T. Vermeulen.
6 *
7 * See COPYING for copyright license. If you did not receive a file called
8 * COPYING with this source code, please notify the distributor of this
9 * mistake, or contact the author.
10 */
11#ifndef PQXX_H_SEPARATED_LIST
12#define PQXX_H_SEPARATED_LIST
13
14#if !defined(PQXX_HEADER_PRE)
15# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
16#endif
17
18#include <algorithm>
19#include <numeric>
20
21#include "pqxx/strconv.hxx"
22
23// C++20: Simplify using std::ranges::range.
24// C++20: Optimise buffer allocation using random_access_range/iterator.
25namespace pqxx
26{
31
33
41template<typename ITER, typename ACCESS>
42[[nodiscard]] inline std::string
43separated_list(std::string_view sep, ITER begin, ITER end, ACCESS access)
44{
45 if (end == begin)
46 return {};
47 auto next{begin};
48 ++next;
49 if (next == end)
50 return to_string(access(begin));
51
52 // From here on, we've got at least 2 elements -- meaning that we need sep.
53 using elt_type = strip_t<decltype(access(begin))>;
54 using traits = string_traits<elt_type>;
55
56 std::size_t budget{0};
57 for (ITER cnt{begin}; cnt != end; ++cnt)
58 budget += traits::size_buffer(access(cnt));
59 budget +=
60 static_cast<std::size_t>(std::distance(begin, end)) * std::size(sep);
61
62 std::string result;
63 result.resize(budget);
64
65 char *const data{result.data()};
66 char *here{data};
67 char *stop{data + budget};
68 here = traits::into_buf(here, stop, access(begin)) - 1;
69 for (++begin; begin != end; ++begin)
70 {
71 here += sep.copy(here, std::size(sep));
72 here = traits::into_buf(here, stop, access(begin)) - 1;
73 }
74 result.resize(static_cast<std::size_t>(here - data));
75 return result;
76}
77
78
80template<typename ITER>
81[[nodiscard]] inline std::string
82separated_list(std::string_view sep, ITER begin, ITER end)
83{
84 return separated_list(sep, begin, end, [](ITER i) { return *i; });
85}
86
87
89template<typename CONTAINER>
90[[nodiscard]] inline auto
91separated_list(std::string_view sep, CONTAINER const &c)
92 /*
93 Always std::string; necessary because SFINAE doesn't work with the
94 contents of function bodies, so the check for iterability has to be in
95 the signature.
96 */
97 -> typename std::enable_if<
98 (not std::is_void<decltype(std::begin(c))>::value and
99 not std::is_void<decltype(std::end(c))>::value),
100 std::string>::type
101{
102 return separated_list(sep, std::begin(c), std::end(c));
103}
104
105
107template<
108 typename TUPLE, std::size_t INDEX = 0, typename ACCESS,
109 typename std::enable_if<
110 (INDEX == std::tuple_size<TUPLE>::value - 1), int>::type = 0>
111[[nodiscard]] inline std::string separated_list(
112 std::string_view /* sep */, TUPLE const &t, ACCESS const &access)
113{
114 return to_string(access(&std::get<INDEX>(t)));
115}
116
117template<
118 typename TUPLE, std::size_t INDEX = 0, typename ACCESS,
119 typename std::enable_if<
120 (INDEX < std::tuple_size<TUPLE>::value - 1), int>::type = 0>
121[[nodiscard]] inline std::string
122separated_list(std::string_view sep, TUPLE const &t, ACCESS const &access)
123{
124 std::string out{to_string(access(&std::get<INDEX>(t)))};
125 out.append(sep);
126 out.append(separated_list<TUPLE, INDEX + 1>(sep, t, access));
127 return out;
128}
129
130template<
131 typename TUPLE, std::size_t INDEX = 0,
132 typename std::enable_if<
133 (INDEX <= std::tuple_size<TUPLE>::value), int>::type = 0>
134[[nodiscard]] inline std::string
135separated_list(std::string_view sep, TUPLE const &t)
136{
137 // TODO: Optimise allocation.
138 return separated_list(sep, t, [](TUPLE const &tup) { return *tup; });
139}
141} // namespace pqxx
142#endif
The home of all libpqxx classes, functions, templates, etc.
Definition array.hxx:27
std::string separated_list(std::string_view sep, ITER begin, ITER end, ACCESS access)
Represent sequence of values as a string, joined by a given separator.
Definition separated_list.hxx:43
std::remove_cv_t< std::remove_reference_t< TYPE > > strip_t
Remove any constness, volatile, and reference-ness from a type.
Definition types.hxx:91
std::string to_string(field const &value)
Convert a field to a string.
Definition result.cxx:533
Result set containing data returned by a query or command.
Definition result.hxx:74
Traits class for use in string conversions.
Definition strconv.hxx:155