Issue #16959 has been updated by zverok (Victor Shepelev).


Probably not only specs are "guilty", but also Ruby 2.7's changelog (and maybe, a small bit, [my rendering of it](https://rubyreferences.github.io/rubychanges/2.7.html#objectspaceweakmap-now-accepts-non-gc-able-objects)): it included changes in "private" class as a part of official changelog, and people start noticing it can be used for all kind of stuff...

Though, the ticket #16035 that caused the changelog entry implies that people was _already_ using it. And Matz's answer there goes as:

> I think this is the required behavior for WeakMap to implement a cache for example. Accepted.

(Also implying the class is publicly usable.)

I had clarifying this on my post-2.7 TODO list, but haven't acted on it, yet.

----------------------------------------
Bug #16959: Weakmap has specs and third-party usage despite being a private API
https://bugs.ruby-lang.org/issues/16959#change-86144

* Author: headius (Charles Nutter)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
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Weakmap is still described as an internal API, and the documentation points users at WeakRef as the official public API:

https://github.com/ruby/ruby/blob/1fb16dbb6e28b9f32f92554d29e646e088b21a98/gc.c#L11928-L11936

However there are now specs for its current set of features, even though those features have never been discussed or approved as a public API:

https://github.com/ruby/spec/tree/dd8437628a6f2de5b74b338d4960682bb1590a60/core/objectspace/weakmap

And we are starting to see it being used by the community:

* https://github.com/jruby/jruby/issues/6267
* https://github.com/rsim/oracle-enhanced/issues/2027 
* https://github.com/rails/rails/pull/39121

One of two things needs to happen:

* Weakmap is made a public API after some discussion. It would be an official public feature only in 2.8/3.0 or higher.
* The specs are be removed and Weakmap remains a private API not to be used by the community. I suspect the addition of the specs led to folks starting to use this private API.

(edit: The Rails PR was merged after the specs, but the change is actually a year old, as mentioned below. In any case there's plenty of in-the-wild uses of WeakMap that go back even further.)

Personally, I'm in much more in favor of making WeakRef support all the features necessary to implement Weakmap in pure Ruby, rather than the other way around:

https://bugs.ruby-lang.org/issues/6309

But whatever happens it needs to happen soon, since this use case is now a merged feature in Rails master.



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