Bug 21775 – std.typecons.RefCounted, std.container.array.Array, & similar structs that manage their own memory do not need to be scanned unless GC-allocated memory is reachable through them

Code that manually allocates memory without using the GC is responsible for calling GC.addRange if there is the possibility the memory might contain a pointer through which GC-allocated memory is reachable. Conservatively determining this via std.traits.hasIndirections can lead to false positives when nesting multiple types that manage their own memory, for instance a refcounted array of refcounted items. There is a related problem in the Phobos implementation of std.container.array.Array that affects every Array regardless of its element type. Array!E is shaped like: --- import std.typecons : RefCounted; struct Array(E) { static struct Payload { size_t capacity; E[] payload; // allocated with malloc. /// ... } auto data = RefCounted!Payload; /// ... } --- Because Payload has a pointer to an array, RefCounted!(Array!E.Payload) calls GC.addRange irrespective of E. This situation can be improved. Rather than use a general-purpose check for whether a type has pointers, RefCounted and related types can use a special-purpose slightly altered version that need not be exposed to library users.

@n8sh created dlang/phobos pull request #7923 "std.typecons.RefCounted, std.container.array.Array, & similar structs that manage their own memory do not need to be scanned unless GC-allocated memory is reachable through them" mentioning this issue: - Issue 21775 - std.typecons.RefCounted, std.container.array.Array, & similar structs that manage their own memory do not need to be scanned unless GC-allocated memory is reachable through them https://github.com/dlang/phobos/pull/7923

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