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webrtc_m130/g3doc/abseil-in-webrtc.md
Harald Alvestrand aaaeb29ef5 Allow single-argument StrCat 
and modify DEPS files accordingly.
This is done in support of the decision to encourage AbslStringify.

Bug: None
Change-Id: I26fee77978d1dd21be6d2ef011c4dfd78a7b43e0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/367204
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43338}
2024-10-31 15:31:38 +00:00

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Using Abseil in WebRTC

You may use a subset of the utilities provided by the 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.

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

  • 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.

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 #2015 for details on AbslStringify.