1//
2// Copyright 2017 The Abseil Authors.
3//
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at
7//
8// https://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15//
16// -----------------------------------------------------------------------------
17// File: str_join.h
18// -----------------------------------------------------------------------------
19//
20// This header file contains functions for joining a range of elements and
21// returning the result as a std::string. StrJoin operations are specified by
22// passing a range, a separator string to use between the elements joined, and
23// an optional Formatter responsible for converting each argument in the range
24// to a string. If omitted, a default `AlphaNumFormatter()` is called on the
25// elements to be joined, using the same formatting that `absl::StrCat()` uses.
26// This package defines a number of default formatters, and you can define your
27// own implementations.
28//
29// Ranges are specified by passing a container with `std::begin()` and
30// `std::end()` iterators, container-specific `begin()` and `end()` iterators, a
31// brace-initialized `std::initializer_list`, or a `std::tuple` of heterogeneous
32// objects. The separator string is specified as an `absl::string_view`.
33//
34// Because the default formatter uses the `absl::AlphaNum` class,
35// `absl::StrJoin()`, like `absl::StrCat()`, will work out-of-the-box on
36// collections of strings, ints, floats, doubles, etc.
37//
38// Example:
39//
40// std::vector<std::string> v = {"foo", "bar", "baz"};
41// std::string s = absl::StrJoin(v, "-");
42// EXPECT_EQ("foo-bar-baz", s);
43//
44// See comments on the `absl::StrJoin()` function for more examples.
45
46#ifndef ABSL_STRINGS_STR_JOIN_H_
47#define ABSL_STRINGS_STR_JOIN_H_
48
49#include <cstdio>
50#include <cstring>
51#include <initializer_list>
52#include <iterator>
53#include <string>
54#include <tuple>
55#include <type_traits>
56#include <utility>
57
58#include "absl/base/macros.h"
59#include "absl/strings/internal/str_join_internal.h"
60#include "absl/strings/string_view.h"
61
62namespace absl {
63
64// -----------------------------------------------------------------------------
65// Concept: Formatter
66// -----------------------------------------------------------------------------
67//
68// A Formatter is a function object that is responsible for formatting its
69// argument as a string and appending it to a given output std::string.
70// Formatters may be implemented as function objects, lambdas, or normal
71// functions. You may provide your own Formatter to enable `absl::StrJoin()` to
72// work with arbitrary types.
73//
74// The following is an example of a custom Formatter that simply uses
75// `std::to_string()` to format an integer as a std::string.
76//
77// struct MyFormatter {
78// void operator()(std::string* out, int i) const {
79// out->append(std::to_string(i));
80// }
81// };
82//
83// You would use the above formatter by passing an instance of it as the final
84// argument to `absl::StrJoin()`:
85//
86// std::vector<int> v = {1, 2, 3, 4};
87// std::string s = absl::StrJoin(v, "-", MyFormatter());
88// EXPECT_EQ("1-2-3-4", s);
89//
90// The following standard formatters are provided within this file:
91//
92// - `AlphaNumFormatter()` (the default)
93// - `StreamFormatter()`
94// - `PairFormatter()`
95// - `DereferenceFormatter()`
96
97// AlphaNumFormatter()
98//
99// Default formatter used if none is specified. Uses `absl::AlphaNum` to convert
100// numeric arguments to strings.
101inline strings_internal::AlphaNumFormatterImpl AlphaNumFormatter() {
102 return strings_internal::AlphaNumFormatterImpl();
103}
104
105// StreamFormatter()
106//
107// Formats its argument using the << operator.
108inline strings_internal::StreamFormatterImpl StreamFormatter() {
109 return strings_internal::StreamFormatterImpl();
110}
111
112// Function Template: PairFormatter(Formatter, absl::string_view, Formatter)
113//
114// Formats a `std::pair` by putting a given separator between the pair's
115// `.first` and `.second` members. This formatter allows you to specify
116// custom Formatters for both the first and second member of each pair.
117template <typename FirstFormatter, typename SecondFormatter>
118inline strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>
119PairFormatter(FirstFormatter f1, absl::string_view sep, SecondFormatter f2) {
120 return strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>(
121 std::move(f1), sep, std::move(f2));
122}
123
124// Function overload of PairFormatter() for using a default
125// `AlphaNumFormatter()` for each Formatter in the pair.
126inline strings_internal::PairFormatterImpl<
127 strings_internal::AlphaNumFormatterImpl,
128 strings_internal::AlphaNumFormatterImpl>
129PairFormatter(absl::string_view sep) {
130 return PairFormatter(AlphaNumFormatter(), sep, AlphaNumFormatter());
131}
132
133// Function Template: DereferenceFormatter(Formatter)
134//
135// Formats its argument by dereferencing it and then applying the given
136// formatter. This formatter is useful for formatting a container of
137// pointer-to-T. This pattern often shows up when joining repeated fields in
138// protocol buffers.
139template <typename Formatter>
140strings_internal::DereferenceFormatterImpl<Formatter> DereferenceFormatter(
141 Formatter&& f) {
142 return strings_internal::DereferenceFormatterImpl<Formatter>(
143 std::forward<Formatter>(f));
144}
145
146// Function overload of `DererefenceFormatter()` for using a default
147// `AlphaNumFormatter()`.
148inline strings_internal::DereferenceFormatterImpl<
149 strings_internal::AlphaNumFormatterImpl>
150DereferenceFormatter() {
151 return strings_internal::DereferenceFormatterImpl<
152 strings_internal::AlphaNumFormatterImpl>(AlphaNumFormatter());
153}
154
155// -----------------------------------------------------------------------------
156// StrJoin()
157// -----------------------------------------------------------------------------
158//
159// Joins a range of elements and returns the result as a std::string.
160// `absl::StrJoin()` takes a range, a separator string to use between the
161// elements joined, and an optional Formatter responsible for converting each
162// argument in the range to a string.
163//
164// If omitted, the default `AlphaNumFormatter()` is called on the elements to be
165// joined.
166//
167// Example 1:
168// // Joins a collection of strings. This pattern also works with a collection
169// // of `absl::string_view` or even `const char*`.
170// std::vector<std::string> v = {"foo", "bar", "baz"};
171// std::string s = absl::StrJoin(v, "-");
172// EXPECT_EQ("foo-bar-baz", s);
173//
174// Example 2:
175// // Joins the values in the given `std::initializer_list<>` specified using
176// // brace initialization. This pattern also works with an initializer_list
177// // of ints or `absl::string_view` -- any `AlphaNum`-compatible type.
178// std::string s = absl::StrJoin({"foo", "bar", "baz"}, "-");
179// EXPECT_EQ("foo-bar-baz", s);
180//
181// Example 3:
182// // Joins a collection of ints. This pattern also works with floats,
183// // doubles, int64s -- any `StrCat()`-compatible type.
184// std::vector<int> v = {1, 2, 3, -4};
185// std::string s = absl::StrJoin(v, "-");
186// EXPECT_EQ("1-2-3--4", s);
187//
188// Example 4:
189// // Joins a collection of pointer-to-int. By default, pointers are
190// // dereferenced and the pointee is formatted using the default format for
191// // that type; such dereferencing occurs for all levels of indirection, so
192// // this pattern works just as well for `std::vector<int**>` as for
193// // `std::vector<int*>`.
194// int x = 1, y = 2, z = 3;
195// std::vector<int*> v = {&x, &y, &z};
196// std::string s = absl::StrJoin(v, "-");
197// EXPECT_EQ("1-2-3", s);
198//
199// Example 5:
200// // Dereferencing of `std::unique_ptr<>` is also supported:
201// std::vector<std::unique_ptr<int>> v
202// v.emplace_back(new int(1));
203// v.emplace_back(new int(2));
204// v.emplace_back(new int(3));
205// std::string s = absl::StrJoin(v, "-");
206// EXPECT_EQ("1-2-3", s);
207//
208// Example 6:
209// // Joins a `std::map`, with each key-value pair separated by an equals
210// // sign. This pattern would also work with, say, a
211// // `std::vector<std::pair<>>`.
212// std::map<std::string, int> m = {
213// std::make_pair("a", 1),
214// std::make_pair("b", 2),
215// std::make_pair("c", 3)};
216// std::string s = absl::StrJoin(m, ",", absl::PairFormatter("="));
217// EXPECT_EQ("a=1,b=2,c=3", s);
218//
219// Example 7:
220// // These examples show how `absl::StrJoin()` handles a few common edge
221// // cases:
222// std::vector<std::string> v_empty;
223// EXPECT_EQ("", absl::StrJoin(v_empty, "-"));
224//
225// std::vector<std::string> v_one_item = {"foo"};
226// EXPECT_EQ("foo", absl::StrJoin(v_one_item, "-"));
227//
228// std::vector<std::string> v_empty_string = {""};
229// EXPECT_EQ("", absl::StrJoin(v_empty_string, "-"));
230//
231// std::vector<std::string> v_one_item_empty_string = {"a", ""};
232// EXPECT_EQ("a-", absl::StrJoin(v_one_item_empty_string, "-"));
233//
234// std::vector<std::string> v_two_empty_string = {"", ""};
235// EXPECT_EQ("-", absl::StrJoin(v_two_empty_string, "-"));
236//
237// Example 8:
238// // Joins a `std::tuple<T...>` of heterogeneous types, converting each to
239// // a std::string using the `absl::AlphaNum` class.
240// std::string s = absl::StrJoin(std::make_tuple(123, "abc", 0.456), "-");
241// EXPECT_EQ("123-abc-0.456", s);
242
243template <typename Iterator, typename Formatter>
244std::string StrJoin(Iterator start, Iterator end, absl::string_view sep,
245 Formatter&& fmt) {
246 return strings_internal::JoinAlgorithm(start, end, sep, fmt);
247}
248
249template <typename Range, typename Formatter>
250std::string StrJoin(const Range& range, absl::string_view separator,
251 Formatter&& fmt) {
252 return strings_internal::JoinRange(range, separator, fmt);
253}
254
255template <typename T, typename Formatter>
256std::string StrJoin(std::initializer_list<T> il, absl::string_view separator,
257 Formatter&& fmt) {
258 return strings_internal::JoinRange(il, separator, fmt);
259}
260
261template <typename... T, typename Formatter>
262std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator,
263 Formatter&& fmt) {
264 return strings_internal::JoinAlgorithm(value, separator, fmt);
265}
266
267template <typename Iterator>
268std::string StrJoin(Iterator start, Iterator end, absl::string_view separator) {
269 return strings_internal::JoinRange(start, end, separator);
270}
271
272template <typename Range>
273std::string StrJoin(const Range& range, absl::string_view separator) {
274 return strings_internal::JoinRange(range, separator);
275}
276
277template <typename T>
278std::string StrJoin(std::initializer_list<T> il, absl::string_view separator) {
279 return strings_internal::JoinRange(il, separator);
280}
281
282template <typename... T>
283std::string StrJoin(const std::tuple<T...>& value,
284 absl::string_view separator) {
285 return strings_internal::JoinAlgorithm(value, separator, AlphaNumFormatter());
286}
287
288} // namespace absl
289
290#endif // ABSL_STRINGS_STR_JOIN_H_
291