virtual_ptr: allow a virtual_ptr to the class as a member of the class - #109
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struct Node {
virtual ~Node() = default;
virtual_ptr<Node> next;
};
failed to compile with gcc 16: `invalid use of incomplete type 'struct
Node'`, from `std::is_polymorphic_v<Node>`. Three member templates of
`virtual_ptr` - the constructor from `Other*`, and the assignments from
`Other&` and `Other*` - constrained themselves with
`IsPolymorphic<Class, Registry> && std::is_constructible_v<Class*, Other*>`
in a default template argument. The first operand does not depend on `Other`,
so gcc evaluates it when the class itself is instantiated - for the member
declaration, where `Node` is still incomplete. libstdc++ 13 answered
`is_polymorphic` on an incomplete type; 16 rejects it, as the standard allows.
The check now names `Other`, through an ignored trailing pack on the
exposition-only `IsPolymorphic`, which makes it dependent and defers it to the
first use of the member - where the class is complete. And it sits in a
defaulted parameter of its own, after the pointer-convertibility test: clang
reaches these candidates during overload resolution for the member's implicit
copy assignment, with `Other` = `const virtual_ptr<Node>`, and substitution
stops at the first condition that fails. That is the shape CLAUDE.md
prescribes for MrDocs anyway, and the rendered constraint reads the same.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MDgWtJsC4KihJHq73cuCcV
|
An automated preview of the documentation is available at https://109.openmethod.prtest3.cppalliance.org/libs/openmethod/doc/html/index.html If more commits are pushed to the pull request, the docs will rebuild at the same URL. 2026-09-13 17:27:11 UTC |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## develop #109 +/- ##
===========================================
- Coverage 93.62% 93.51% -0.12%
===========================================
Files 22 22
Lines 1694 1695 +1
Branches 505 504 -1
===========================================
- Hits 1586 1585 -1
- Misses 64 66 +2
Partials 44 44
... and 1 file with indirect coverage changes Continue to review full report in Codecov by Harness.
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failed to compile with gcc 16:
invalid use of incomplete type 'struct Node', fromstd::is_polymorphic_v<Node>.Three member templates of
virtual_ptr— the constructor fromOther*, and the assignments fromOther&andOther*— constrained themselves withIsPolymorphic<Class, Registry> && std::is_constructible_v<Class*, Other*>in a default templateargument. The first operand does not depend on
Other, so gcc evaluates it when the class itselfis instantiated — for the member declaration, where
Nodeis still incomplete. libstdc++ 13answered
is_polymorphicon an incomplete type; 16 rejects it, as the standard allows.The check now names
Other, through an ignored trailing pack on the exposition-onlyIsPolymorphic, which makes it dependent and defers it to the first use of the member — where theclass is complete. And it sits in a defaulted parameter of its own, after the pointer-convertibility
test: clang reaches these candidates during overload resolution for the member's implicit copy
assignment, with
Other=const virtual_ptr<Node>, and substitution stops at the first conditionthat fails. That is the shape CLAUDE.md prescribes for MrDocs anyway, and the rendered constraint
reads the same.
test/test_virtual_ptr_self_referential.cppcovers the case. Full suite: 165/165 pass locally.🤖 Generated with Claude Code
https://claude.ai/code/session_01JQa4fuiwcfsheZYTCyfPPr