Why is absl::base_internal::invoke in the internal namespace?

[pfaion]

Hi everyone, thanks for making and maintaining this great library!

I am using abseil in a C++14 codebase to get support for newer C++ features. I find myself frequently wanting to use std::invoke, which is a C++17 feature. Looking into abseil, I found absl/base/internal/invoke.h, which implements a version of std::invoke. However, this implementation is placed into the internal namespace as absl::base_internal::invoke, which AFAIK should not be used from the outside.

1. Is there a specific reason for that?
2. Is there a plan to implement something like absl::invoke outside of the internal namespace?

[derekmauro]

Hi everyone, thanks for making and maintaining this great library!

I am using abseil in a C++14 codebase to get support for newer C++ features. I find myself frequently wanting to use std::invoke, which is a C++17 feature. Looking into abseil, I found absl/base/internal/invoke.h, which implements a version of std::invoke. However, this implementation is placed into the internal namespace as absl::base_internal::invoke, which AFAIK should not be used from the outside.

1. Is there a specific reason for that?

Abseil's primary purpose is to be used as a dependency by Google's open source C++ projects. This means that Abseil contains the most used pieces of what was once our internal-only codebase. absl::base_internal::invoke actually wasn't used at all, so it was not battle-tested by thousands of callers. It was only needed as an implementation detail for a handful of other types. Once you add something to your public API surface it becomes a maintenance cost, so we decided not to do that.

2. Is there a plan to implement something like absl::invoke outside of the internal namespace?

No. Google-internal is on C++17 now, so we have std::invoke. We only add polyfills that we need ourselves.

[pfaion]

Thank you for the detailed response!