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tubestation/third_party/libwebrtc/g3doc/abseil-in-webrtc.md
Michael Froman 38b795f76f Bug 1942428 - Vendor libwebrtc from d004aee4a4 
Upstream commit: https://webrtc.googlesource.com/src/+/d004aee4a41f3fba3b29ef33be2c4f07f2ceb1e7
    Allow absl map and set containers in WebRTC


    Bug: None
    No-Try: True
    Change-Id: I84218daf71de115af74e0484bc26e798f125297a
    Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/370762
    Reviewed-by: Harald Alvestrand <hta@webrtc.org>
    Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
    Cr-Commit-Position: refs/heads/main@{#43529}
2025-02-07 15:08:54 -06:00

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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

  • Hash tables, and B-tree ordered 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.

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 for details on AbslStringify.