P3171 R0 Adding functionality to placeholder types

[wg21bot]

P3171R0 Adding functionality to placeholder types (Barry Revzin, Peter Dimov)

[ben-craig]

2024-06-04 Library Evolution Telecon

P3171R0: Adding functionality to placeholder types

2024-06-04 Library Evolution Telecon Minutes

Champion: Barry Revzin
Chair: Ben Craig
Minute Taker: Mark Hoemmen

Summary

Maybe make op[] and subscript multidimensional?
Talks about addrof, doesn't talk about simple assignment.
Consider semantics of op(). Why is it pack indexing instead of forwarding to underlying call operator?
Consider making std::get work in addition or instead of first and second.
Discuss why op->*s semantics aren't the "obvious" thing.

Discuss providing customization point so user streaming operators (op<< and op>>) can work. Maybe generalize this elsewhere for domain specific languages.

Recommend adding example involving binary predicate, like std::sort, so we can see _2 usage in addition to _1.
Discuss repeated placeholders (e.g. _1 + _1). Do they have double move issues?

Provide further motivation for logical and and or and discuss short circuiting, particularly around nested binds.

33: should be Notes

POLL: We should promise more committee time to pursuing Adding functionality to placeholder types, knowing that our time is scarce and this will leave less time for other work.

SF	WF	N	WA	SA
1	9	4	1	0

Attendance: 19

# of Authors: 1

Author Position: SF

Outcome: Consensus in favor

Comments: WA: not clear on the value this is adding to the standard, vs in a library.

POLL: Spend more time on operators for placeholders

SF	WF	N	WA	SA
1	4	6	1	1

Attendance: 20

# of Authors: 1

Author Position: SF

Outcome: No consensus

Comments:

POLL: Spend more time on function objects

SF	WF	N	WA	SA
4	7	2	0	0

Attendance: 20

# of Authors: 1

Author Position: SF

Outcome: Consensus

Comments:

Next Steps

Bring a new revision addressing and/or discussing the above feedback.