fc8dc48020
git-subtree-dir: third_party/abseil_cpp git-subtree-mainline:ffb2ae54begit-subtree-split:768eb2ca28
293 lines
11 KiB
C++
293 lines
11 KiB
C++
//
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: str_join.h
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// -----------------------------------------------------------------------------
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//
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// This header file contains functions for joining a range of elements and
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// returning the result as a std::string. StrJoin operations are specified by
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// passing a range, a separator string to use between the elements joined, and
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// an optional Formatter responsible for converting each argument in the range
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// to a string. If omitted, a default `AlphaNumFormatter()` is called on the
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// elements to be joined, using the same formatting that `absl::StrCat()` uses.
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// This package defines a number of default formatters, and you can define your
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// own implementations.
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//
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// Ranges are specified by passing a container with `std::begin()` and
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// `std::end()` iterators, container-specific `begin()` and `end()` iterators, a
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// brace-initialized `std::initializer_list`, or a `std::tuple` of heterogeneous
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// objects. The separator string is specified as an `absl::string_view`.
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//
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// Because the default formatter uses the `absl::AlphaNum` class,
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// `absl::StrJoin()`, like `absl::StrCat()`, will work out-of-the-box on
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// collections of strings, ints, floats, doubles, etc.
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//
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// Example:
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//
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// std::vector<std::string> v = {"foo", "bar", "baz"};
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// std::string s = absl::StrJoin(v, "-");
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// EXPECT_EQ("foo-bar-baz", s);
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//
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// See comments on the `absl::StrJoin()` function for more examples.
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#ifndef ABSL_STRINGS_STR_JOIN_H_
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#define ABSL_STRINGS_STR_JOIN_H_
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#include <cstdio>
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#include <cstring>
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#include <initializer_list>
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#include <iterator>
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#include <string>
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#include <tuple>
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#include <type_traits>
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#include <utility>
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#include "absl/base/macros.h"
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#include "absl/strings/internal/str_join_internal.h"
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#include "absl/strings/string_view.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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// -----------------------------------------------------------------------------
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// Concept: Formatter
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// -----------------------------------------------------------------------------
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//
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// A Formatter is a function object that is responsible for formatting its
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// argument as a string and appending it to a given output std::string.
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// Formatters may be implemented as function objects, lambdas, or normal
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// functions. You may provide your own Formatter to enable `absl::StrJoin()` to
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// work with arbitrary types.
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//
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// The following is an example of a custom Formatter that simply uses
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// `std::to_string()` to format an integer as a std::string.
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//
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// struct MyFormatter {
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// void operator()(std::string* out, int i) const {
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// out->append(std::to_string(i));
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// }
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// };
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//
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// You would use the above formatter by passing an instance of it as the final
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// argument to `absl::StrJoin()`:
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//
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// std::vector<int> v = {1, 2, 3, 4};
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// std::string s = absl::StrJoin(v, "-", MyFormatter());
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// EXPECT_EQ("1-2-3-4", s);
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//
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// The following standard formatters are provided within this file:
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//
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// - `AlphaNumFormatter()` (the default)
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// - `StreamFormatter()`
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// - `PairFormatter()`
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// - `DereferenceFormatter()`
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// AlphaNumFormatter()
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//
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// Default formatter used if none is specified. Uses `absl::AlphaNum` to convert
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// numeric arguments to strings.
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inline strings_internal::AlphaNumFormatterImpl AlphaNumFormatter() {
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return strings_internal::AlphaNumFormatterImpl();
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}
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// StreamFormatter()
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//
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// Formats its argument using the << operator.
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inline strings_internal::StreamFormatterImpl StreamFormatter() {
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return strings_internal::StreamFormatterImpl();
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}
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// Function Template: PairFormatter(Formatter, absl::string_view, Formatter)
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//
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// Formats a `std::pair` by putting a given separator between the pair's
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// `.first` and `.second` members. This formatter allows you to specify
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// custom Formatters for both the first and second member of each pair.
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template <typename FirstFormatter, typename SecondFormatter>
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inline strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>
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PairFormatter(FirstFormatter f1, absl::string_view sep, SecondFormatter f2) {
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return strings_internal::PairFormatterImpl<FirstFormatter, SecondFormatter>(
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std::move(f1), sep, std::move(f2));
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}
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// Function overload of PairFormatter() for using a default
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// `AlphaNumFormatter()` for each Formatter in the pair.
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inline strings_internal::PairFormatterImpl<
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strings_internal::AlphaNumFormatterImpl,
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strings_internal::AlphaNumFormatterImpl>
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PairFormatter(absl::string_view sep) {
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return PairFormatter(AlphaNumFormatter(), sep, AlphaNumFormatter());
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}
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// Function Template: DereferenceFormatter(Formatter)
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//
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// Formats its argument by dereferencing it and then applying the given
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// formatter. This formatter is useful for formatting a container of
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// pointer-to-T. This pattern often shows up when joining repeated fields in
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// protocol buffers.
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template <typename Formatter>
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strings_internal::DereferenceFormatterImpl<Formatter> DereferenceFormatter(
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Formatter&& f) {
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return strings_internal::DereferenceFormatterImpl<Formatter>(
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std::forward<Formatter>(f));
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}
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// Function overload of `DererefenceFormatter()` for using a default
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// `AlphaNumFormatter()`.
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inline strings_internal::DereferenceFormatterImpl<
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strings_internal::AlphaNumFormatterImpl>
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DereferenceFormatter() {
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return strings_internal::DereferenceFormatterImpl<
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strings_internal::AlphaNumFormatterImpl>(AlphaNumFormatter());
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}
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// -----------------------------------------------------------------------------
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// StrJoin()
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// -----------------------------------------------------------------------------
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//
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// Joins a range of elements and returns the result as a std::string.
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// `absl::StrJoin()` takes a range, a separator string to use between the
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// elements joined, and an optional Formatter responsible for converting each
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// argument in the range to a string.
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//
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// If omitted, the default `AlphaNumFormatter()` is called on the elements to be
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// joined.
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//
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// Example 1:
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// // Joins a collection of strings. This pattern also works with a collection
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// // of `absl::string_view` or even `const char*`.
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// std::vector<std::string> v = {"foo", "bar", "baz"};
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// std::string s = absl::StrJoin(v, "-");
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// EXPECT_EQ("foo-bar-baz", s);
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//
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// Example 2:
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// // Joins the values in the given `std::initializer_list<>` specified using
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// // brace initialization. This pattern also works with an initializer_list
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// // of ints or `absl::string_view` -- any `AlphaNum`-compatible type.
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// std::string s = absl::StrJoin({"foo", "bar", "baz"}, "-");
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// EXPECT_EQ("foo-bar-baz", s);
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//
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// Example 3:
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// // Joins a collection of ints. This pattern also works with floats,
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// // doubles, int64s -- any `StrCat()`-compatible type.
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// std::vector<int> v = {1, 2, 3, -4};
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// std::string s = absl::StrJoin(v, "-");
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// EXPECT_EQ("1-2-3--4", s);
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//
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// Example 4:
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// // Joins a collection of pointer-to-int. By default, pointers are
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// // dereferenced and the pointee is formatted using the default format for
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// // that type; such dereferencing occurs for all levels of indirection, so
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// // this pattern works just as well for `std::vector<int**>` as for
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// // `std::vector<int*>`.
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// int x = 1, y = 2, z = 3;
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// std::vector<int*> v = {&x, &y, &z};
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// std::string s = absl::StrJoin(v, "-");
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// EXPECT_EQ("1-2-3", s);
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//
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// Example 5:
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// // Dereferencing of `std::unique_ptr<>` is also supported:
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// std::vector<std::unique_ptr<int>> v
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// v.emplace_back(new int(1));
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// v.emplace_back(new int(2));
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// v.emplace_back(new int(3));
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// std::string s = absl::StrJoin(v, "-");
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// EXPECT_EQ("1-2-3", s);
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//
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// Example 6:
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// // Joins a `std::map`, with each key-value pair separated by an equals
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// // sign. This pattern would also work with, say, a
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// // `std::vector<std::pair<>>`.
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// std::map<std::string, int> m = {
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// std::make_pair("a", 1),
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// std::make_pair("b", 2),
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// std::make_pair("c", 3)};
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// std::string s = absl::StrJoin(m, ",", absl::PairFormatter("="));
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// EXPECT_EQ("a=1,b=2,c=3", s);
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//
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// Example 7:
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// // These examples show how `absl::StrJoin()` handles a few common edge
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// // cases:
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// std::vector<std::string> v_empty;
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// EXPECT_EQ("", absl::StrJoin(v_empty, "-"));
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//
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// std::vector<std::string> v_one_item = {"foo"};
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// EXPECT_EQ("foo", absl::StrJoin(v_one_item, "-"));
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//
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// std::vector<std::string> v_empty_string = {""};
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// EXPECT_EQ("", absl::StrJoin(v_empty_string, "-"));
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//
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// std::vector<std::string> v_one_item_empty_string = {"a", ""};
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// EXPECT_EQ("a-", absl::StrJoin(v_one_item_empty_string, "-"));
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//
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// std::vector<std::string> v_two_empty_string = {"", ""};
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// EXPECT_EQ("-", absl::StrJoin(v_two_empty_string, "-"));
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//
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// Example 8:
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// // Joins a `std::tuple<T...>` of heterogeneous types, converting each to
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// // a std::string using the `absl::AlphaNum` class.
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// std::string s = absl::StrJoin(std::make_tuple(123, "abc", 0.456), "-");
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// EXPECT_EQ("123-abc-0.456", s);
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template <typename Iterator, typename Formatter>
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std::string StrJoin(Iterator start, Iterator end, absl::string_view sep,
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Formatter&& fmt) {
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return strings_internal::JoinAlgorithm(start, end, sep, fmt);
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}
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template <typename Range, typename Formatter>
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std::string StrJoin(const Range& range, absl::string_view separator,
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Formatter&& fmt) {
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return strings_internal::JoinRange(range, separator, fmt);
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}
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template <typename T, typename Formatter>
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std::string StrJoin(std::initializer_list<T> il, absl::string_view separator,
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Formatter&& fmt) {
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return strings_internal::JoinRange(il, separator, fmt);
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}
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template <typename... T, typename Formatter>
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std::string StrJoin(const std::tuple<T...>& value, absl::string_view separator,
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Formatter&& fmt) {
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return strings_internal::JoinAlgorithm(value, separator, fmt);
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}
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template <typename Iterator>
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std::string StrJoin(Iterator start, Iterator end, absl::string_view separator) {
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return strings_internal::JoinRange(start, end, separator);
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}
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template <typename Range>
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std::string StrJoin(const Range& range, absl::string_view separator) {
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return strings_internal::JoinRange(range, separator);
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}
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template <typename T>
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std::string StrJoin(std::initializer_list<T> il,
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absl::string_view separator) {
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return strings_internal::JoinRange(il, separator);
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}
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template <typename... T>
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std::string StrJoin(const std::tuple<T...>& value,
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absl::string_view separator) {
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return strings_internal::JoinAlgorithm(value, separator, AlphaNumFormatter());
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}
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_STRINGS_STR_JOIN_H_
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