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authorGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
committerGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
commitc2e754829628d1e9b7a16b3389cfdace76950fdf (patch)
tree5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/strings/str_join.h
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+//
+// 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_