# Using Abseil in WebRTC You may use a subset of the utilities provided by the [Abseil][abseil] library when writing WebRTC C++ code. Below, we list the explicitly *allowed* and the explicitly *disallowed* subsets of Abseil; if you find yourself in need of something that isn’t in either subset, please add it to the *allowed* subset in this doc in the same CL that adds the first use. [abseil]: https://abseil.io/about/ ## How to depend on Abseil For build targets of type `rtc_library`, `rtc_source_set` and `rtc_static_library`, dependencies on Abseil need to be listed in `deps`. The GN templates will take care of generating the proper dependency when used within Chromium or standalone. In that build mode, WebRTC will depend on a monolithic Abseil build target that will generate a shared library. ## **Allowed** * `absl::AnyInvocable` * `absl::bind_front` * `absl::Cleanup` * [Hash tables, and B-tree ordered][abseil-containers] containers * `absl::InlinedVector` * `absl::Nonnull` and `absl::Nullable` * `absl::WrapUnique` * `absl::string_view` * The functions in `absl/strings/ascii.h`, `absl/strings/match.h`, and `absl/strings/str_replace.h`. * The functions in `absl/strings/escaping.h`. * `absl::is_trivially_copy_constructible`, `absl::is_trivially_copy_assignable`, and `absl::is_trivially_destructible` from `absl/meta/type_traits.h`. * `absl::variant` and related stuff from `absl/types/variant.h`. * The functions in `absl/algorithm/algorithm.h` and `absl/algorithm/container.h`. * `absl/base/const_init.h` for mutex initialization. * The macros in `absl/base/attributes.h`, `absl/base/config.h` and `absl/base/macros.h`. * `absl/numeric/bits.h` * Single argument absl::StrCat * ABSL_FLAG is allowed in tests and tools, but disallowed in in non-test code. [abseil-containers]: https://abseil.io/docs/cpp/guides/container ## **Disallowed** ### `absl::make_unique` *Use `std::make_unique` instead.* ### `absl::Mutex` *Use `webrtc::Mutex` instead.* ### `absl::optional` *Use `std::optional` instead.* ### `absl::Span` *Use `rtc::ArrayView` instead.* `absl::Span` differs from `rtc::ArrayView` on several points, and both of them differ from the `std::span` introduced in C++20. We should just keep using `rtc::ArrayView` and avoid `absl::Span`. When WebRTC switches to C++20, we will consider replacing `rtc::ArrayView` with `std::span`. ### `absl::StrCat`, `absl::StrAppend`, `absl::StrJoin`, `absl::StrSplit` *Use `rtc::SimpleStringBuilder` to build strings.* These are optimized for speed, not binary size. Even `StrCat` calls with a modest number of arguments can easily add several hundred bytes to the binary. Exception: Single-argument absl::StrCat is allowed in order to make it easy to use AbslStringify. See [TOTW #215](https://abseil.io/tips/215) for details on AbslStringify.