Bug 18848 – std.allocator: Regions are non-copyable, yet are passed around in examples

Here is an example from std.experimental.allocator.building_blocks.allocator_list.AllocatorList: // Ouroboros allocator list based upon 4MB regions, fetched directly from // mmap. All memory is released upon destruction. alias A1 = AllocatorList!((n) => Region!MmapAllocator(max(n, 1024 * 4096)), NullAllocator); The example features a lambda returning a Region. However, Regions cannot be copied, as they have a destructor which deallocates everything. A comment in the implementation says: /* TODO: The postblit of $(D BasicRegion) should be disabled because such objects should not be copied around naively. */ (That's the only occurrence of BasicRegion in Phobos, so I assume that's just an old name for Region.) Though NRVO may make the verbatim example code behave correctly, it is fragile, and small code modifications e.g. to work around issue 18848 can cause difficult-to-debug problems (due to dangling pointers in other Region instances).

https://github.com/dlang/phobos/pull/6509 See the comment there for more discussion.

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