Issue 17564: Eliminate "static this" for theAllocator

[s-ludwig]

This switches to lazy initialization of theAllocator, so that accessing it form within shared static this works as expected.

[dlang-bot]

Thanks for your pull request, @s-ludwig!

Bugzilla references

Fix	Bugzilla	Description
✓	17564	std.experimental.allocator.theAllocator is null within shared static this

[wilzbach]

LGTM - how about targeting stable, s.t. it's part of the 2.075.0 release?

[s-ludwig]

LGTM - how about targeting stable, s.t. it's part of the 2.075.0 release?

I originally did that, but then decided on master because it's not a regression. But thinking about it, it would simplify the matching vibe.d fix quite a lot.

[JackStouffer]

Please no enhancements on stable.

[JackStouffer]

Please make this private so people can't access it before it's initialized

[wilzbach]

Please no enhancements on stable.

Excerpt from Bugzilla:

vibe.d needs to use "shared static this" for initialization to support the original initialization scheme for applications that it still in wide use. With 2.075.0-b1, since processAllocator now returns an ISharedAllocator, it had to switch to theAllocator where possible. However, since this returns null during the "shared static this" phase, this causes a crash on startup.

This sounds more like a blocking issue, not an enhancement ;-)

[MartinNowak]

Please no enhancements on stable.

Good reminder.
Low-risk bug fixes are wanted though, in particular during a beta.

[wilzbach]

continuous-integration/jenkins/pr-merge — This commit cannot be built

CC @CyberShadow - yet another PR that hangs in the queue due to the project tester failures :/