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Diffstat (limited to 'absl/strings/str_join.h')
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diff --git a/absl/strings/str_join.h b/absl/strings/str_join.h new file mode 100644 index 00000000..82a3cac2 --- /dev/null +++ b/absl/strings/str_join.h @@ -0,0 +1,288 @@ +// +// Copyright 2017 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// ----------------------------------------------------------------------------- +// File: str_join.h +// ----------------------------------------------------------------------------- +// +// This header file contains functions for joining a range of elements and +// returning the result as a std::string. StrJoin operations are specified by passing +// a range, a separator std::string to use between the elements joined, and an +// optional Formatter responsible for converting each argument in the range to a +// std::string. If omitted, a default `AlphaNumFormatter()` is called on the elements +// to be joined, using the same formatting that `absl::StrCat()` uses. This +// package defines a number of default formatters, and you can define your own +// implementations. +// +// Ranges are specified by passing a container with `std::begin()` and +// `std::end()` iterators, container-specific `begin()` and `end()` iterators, a +// brace-initialized `std::initializer_list`, or a `std::tuple` of heterogeneous +// objects. The separator std::string is specified as an `absl::string_view`. +// +// Because the default formatter uses the `absl::AlphaNum` class, +// `absl::StrJoin()`, like `absl::StrCat()`, will work out-of-the-box on +// collections of strings, ints, floats, doubles, etc. +// +// Example: +// +// std::vector<std::string> v = {"foo", "bar", "baz"}; +// std::string s = absl::StrJoin(v, "-"); +// EXPECT_EQ("foo-bar-baz", s); +// +// See comments on the `absl::StrJoin()` function for more examples. + +#ifndef ABSL_STRINGS_STR_JOIN_H_ +#define ABSL_STRINGS_STR_JOIN_H_ + +#include <cstdio> +#include <cstring> +#include <initializer_list> +#include <iterator> +#include <string> +#include <tuple> +#include <utility> + +#include "absl/base/macros.h" +#include "absl/strings/internal/str_join_internal.h" +#include "absl/strings/string_view.h" + +namespace absl { + +// ----------------------------------------------------------------------------- +// Concept: Formatter +// ----------------------------------------------------------------------------- +// +// A Formatter is a function object that is responsible for formatting its +// argument as a std::string and appending it to a given output std::string. Formatters +// may be implemented as function objects, lambdas, or normal functions. You may +// provide your own Formatter to enable `absl::StrJoin()` to work with arbitrary +// types. +// +// The following is an example of a custom Formatter that simply uses +// `std::to_string()` to format an integer as a std::string. +// +// struct MyFormatter { +// void operator()(std::string* out, int i) const { +// out->append(std::to_string(i)); +// } +// }; +// +// You would use the above formatter by passing an instance of it as the final +// argument to `absl::StrJoin()`: +// +// std::vector<int> v = {1, 2, 3, 4}; +// std::string s = absl::StrJoin(v, "-", MyFormatter()); +// EXPECT_EQ("1-2-3-4", s); +// +// The following standard formatters are provided within this file: +// +// - `AlphaNumFormatter()` (the default) +// - `StreamFormatter()` +// - `PairFormatter()` +// - `DereferenceFormatter()` + +// AlphaNumFormatter() +// +// Default formatter used if none is specified. Uses `absl::AlphaNum` to convert +// numeric arguments to strings. +inline strings_internal::AlphaNumFormatterImpl AlphaNumFormatter() { + return strings_internal::AlphaNumFormatterImpl(); +} + +// StreamFormatter() +// +// Formats its argument using the << operator. +inline strings_internal::StreamFormatterImpl StreamFormatter() { + return strings_internal::StreamFormatterImpl(); +} + +// Function Template: PairFormatter(Formatter, absl::string_view, Formatter) +// +// Formats a `std::pair` by putting a given separator between the pair's +// `.first` and `.second` members. This formatter allows you to specify +// custom Formatters for both the first and second member of each pair. +template <typename FirstFormatter, typename SecondFormatter> +inline strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter> +PairFormatter(FirstFormatter f1, absl::string_view sep, SecondFormatter f2) { + return strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>( + std::move(f1), sep, std::move(f2)); +} + +// Function overload of PairFormatter() for using a default +// `AlphaNumFormatter()` for each Formatter in the pair. +inline strings_internal::PairFormatterImpl< + strings_internal::AlphaNumFormatterImpl, + strings_internal::AlphaNumFormatterImpl> +PairFormatter(absl::string_view sep) { + return PairFormatter(AlphaNumFormatter(), sep, AlphaNumFormatter()); +} + +// Function Template: DereferenceFormatter(Formatter) +// +// Formats its argument by dereferencing it and then applying the given +// formatter. This formatter is useful for formatting a container of +// pointer-to-T. This pattern often shows up when joining repeated fields in +// protocol buffers. +template <typename Formatter> +strings_internal::DereferenceFormatterImpl<Formatter> DereferenceFormatter( + Formatter&& f) { + return strings_internal::DereferenceFormatterImpl<Formatter>( + std::forward<Formatter>(f)); +} + +// Function overload of `DererefenceFormatter()` for using a default +// `AlphaNumFormatter()`. +inline strings_internal::DereferenceFormatterImpl< + strings_internal::AlphaNumFormatterImpl> +DereferenceFormatter() { + return strings_internal::DereferenceFormatterImpl< + strings_internal::AlphaNumFormatterImpl>(AlphaNumFormatter()); +} + +// ----------------------------------------------------------------------------- +// StrJoin() +// ----------------------------------------------------------------------------- +// +// Joins a range of elements and returns the result as a std::string. +// `absl::StrJoin()` takes a range, a separator std::string to use between the +// elements joined, and an optional Formatter responsible for converting each +// argument in the range to a std::string. +// +// If omitted, the default `AlphaNumFormatter()` is called on the elements to be +// joined. +// +// Example 1: +// // Joins a collection of strings. This pattern also works with a collection +// // of `asbl::string_view` or even `const char*`. +// std::vector<std::string> v = {"foo", "bar", "baz"}; +// std::string s = absl::StrJoin(v, "-"); +// EXPECT_EQ("foo-bar-baz", s); +// +// Example 2: +// // Joins the values in the given `std::initializer_list<>` specified using +// // brace initialization. This pattern also works with an initializer_list +// // of ints or `absl::string_view` -- any `AlphaNum`-compatible type. +// std::string s = absl::StrJoin({"foo", "bar", "baz"}, "-"); +// EXPECT_EQ("foo-bar-baz", s); +// +// Example 3: +// // Joins a collection of ints. This pattern also works with floats, +// // doubles, int64s -- any `StrCat()`-compatible type. +// std::vector<int> v = {1, 2, 3, -4}; +// std::string s = absl::StrJoin(v, "-"); +// EXPECT_EQ("1-2-3--4", s); +// +// Example 4: +// // Joins a collection of pointer-to-int. By default, pointers are +// // dereferenced and the pointee is formatted using the default format for +// // that type; such dereferencing occurs for all levels of indirection, so +// // this pattern works just as well for `std::vector<int**>` as for +// // `std::vector<int*>`. +// int x = 1, y = 2, z = 3; +// std::vector<int*> v = {&x, &y, &z}; +// std::string s = absl::StrJoin(v, "-"); +// EXPECT_EQ("1-2-3", s); +// +// Example 5: +// // Dereferencing of `std::unique_ptr<>` is also supported: +// std::vector<std::unique_ptr<int>> v +// v.emplace_back(new int(1)); +// v.emplace_back(new int(2)); +// v.emplace_back(new int(3)); +// std::string s = absl::StrJoin(v, "-"); +// EXPECT_EQ("1-2-3", s); +// +// Example 6: +// // Joins a `std::map`, with each key-value pair separated by an equals +// // sign. This pattern would also work with, say, a +// // `std::vector<std::pair<>>`. +// std::map<std::string, int> m = { +// std::make_pair("a", 1), +// std::make_pair("b", 2), +// std::make_pair("c", 3)}; +// std::string s = absl::StrJoin(m, ",", strings::PairFormatter("=")); +// EXPECT_EQ("a=1,b=2,c=3", s); +// +// Example 7: +// // These examples show how `absl::StrJoin()` handles a few common edge +// // cases: +// std::vector<std::string> v_empty; +// EXPECT_EQ("", absl::StrJoin(v_empty, "-")); +// +// std::vector<std::string> v_one_item = {"foo"}; +// EXPECT_EQ("foo", absl::StrJoin(v_one_item, "-")); +// +// std::vector<std::string> v_empty_string = {""}; +// EXPECT_EQ("", absl::StrJoin(v_empty_string, "-")); +// +// std::vector<std::string> v_one_item_empty_string = {"a", ""}; +// EXPECT_EQ("a-", absl::StrJoin(v_one_item_empty_string, "-")); +// +// std::vector<std::string> v_two_empty_string = {"", ""}; +// EXPECT_EQ("-", absl::StrJoin(v_two_empty_string, "-")); +// +// Example 8: +// // Joins a `std::tuple<T...>` of heterogeneous types, converting each to +// // a std::string using the `absl::AlphaNum` class. +// std::string s = absl::StrJoin(std::make_tuple(123, "abc", 0.456), "-"); +// EXPECT_EQ("123-abc-0.456", s); + +template <typename Iterator, typename Formatter> +std::string StrJoin(Iterator start, Iterator end, absl::string_view sep, + Formatter&& fmt) { + return strings_internal::JoinAlgorithm(start, end, sep, fmt); +} + +template <typename Range, typename Formatter> +std::string StrJoin(const Range& range, absl::string_view separator, + Formatter&& fmt) { + return strings_internal::JoinRange(range, separator, fmt); +} + +template <typename T, typename Formatter> +std::string StrJoin(std::initializer_list<T> il, absl::string_view separator, + Formatter&& fmt) { + return strings_internal::JoinRange(il, separator, fmt); +} + +template <typename... T, typename Formatter> +std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator, + Formatter&& fmt) { + return strings_internal::JoinAlgorithm(value, separator, fmt); +} + +template <typename Iterator> +std::string StrJoin(Iterator start, Iterator end, absl::string_view separator) { + return strings_internal::JoinRange(start, end, separator); +} + +template <typename Range> +std::string StrJoin(const Range& range, absl::string_view separator) { + return strings_internal::JoinRange(range, separator); +} + +template <typename T> +std::string StrJoin(std::initializer_list<T> il, absl::string_view separator) { + return strings_internal::JoinRange(il, separator); +} + +template <typename... T> +std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator) { + return strings_internal::JoinAlgorithm(value, separator, AlphaNumFormatter()); +} + +} // namespace absl + +#endif // ABSL_STRINGS_STR_JOIN_H_ |