P3097 R1 Contracts for C++: Virtual functions

[wg21bot]

P3097R0 Contracts for C++: Support for virtual functions (Timur Doumler, Joshua Berne, Gašper Ažman)

[timuraudio]

Considered by SG21 on 2024-06-13. Needs revision. Direction given:

The Contracts MVP should encourage the principle that you cannot narrow the precondition assertions and you cannot widen the postcondition assertions of an overridden function in an overriding function.
SF F N A SA
2 0 0 8 5
Result: Consensus against

In the Contracts MVP, for a virtual function call, the set of precondition and postcondition assertions that will be checked for a particular overriding function should be independent of how (through which statically called function) that function is called.
SF F N A SA
1 1 1 3 10
Result: Consensus against

The Contracts MVP should offer some mechanism to inherit the precondition and postcondition assertions of an overridden function into functions overriding it.
SF F N A SA
0 2 1 11 1
Result: Consensus against

Contracts should allow pre... (x) and post... (x) on a virtual function where ... are some syntactic markers to explicitly specify them as interface contracts (checked when that function is the statically called function of a virtual function call), implementation contracts (checked when that function's body is executed), or both simultaneously.
SF F N A SA
1 11 2 0 1
Result: Consensus

Contracts should allow unadorned pre (x) and post (x) on a virtual function meaning contract assertions that are simultaneously interface contracts and implementation contracts.
SF F N A SA
5 4 3 1 3
Result: Weak consensus

Contracts should allow unadorned pre (x) and post (x) on a virtual function meaning contract assertions that are implementation contracts.
SF F N A SA
1 1 7 5 2
Result: No consensus

[timuraudio]

Forward pre/post on virtual functions, without additional qualifiers, as proposed in the "Base Proposal" of D3097R1, to EWG, as an extension of P2900, with C++26 as the recommended ship vehicle.

SF F N A SA
10 3 0 2 0

[jfbastien]

Seen in EWG in St Louis:

Poll: P3097R0 — Contracts for C++: Support for Virtual Functions, we are interested in the proposed solution and encourage further work, independent of whether it is in P2900 or not.

SF	F	N	A	SA
23	11	3	5	2

Poll: P3097R0 — Contracts for C++: Support for Virtual Functions, we would like to see this paper merged into P2900 and progress contracts with virtual function support.

SF	F	N	A	SA
18	15	5	1	2

[timuraudio]

P3097R0 absorbed into P2900R8 as directed by EWG in St Louis.